Video summary

Mi Band 9 Pro: Scientific Review (Cheap & Great!?)

Main summary

Key takeaways

Product Review

Product reviewed

Xiaomi Mi Band 9 Pro (fitness tracker). The review focuses on sleep stage tracking, heart-rate tracking, and GPS tracking, and compares it mainly against Mi Band 9 plus various other budget and premium wearables.

Test approach / context

  • Reviewer (Rob) is a post-doctoral scientist who claims a systematic, repeatable testing setup.
  • Most tests were done with the Mi Band 9 Pro using a faux-leather strap.
  • He also bought and tested a rubber-strap version, but reports there weren’t major differences (possibly rubber could be slightly better, but he had limited time).

Key features mentioned

  • Tracks heart rate and sleep.
  • Sleep staging includes 4 stages:
    • Light
    • Deep
    • REM (labeled “RAM sleep” in subtitles)
    • Awake time
  • Has built-in GPS (the main “pro” upgrade vs Mi Band 9).
  • Companion app: Mi Fitness app is mentioned as potentially a positive for user experience.

Heart-rate tracking results (main findings)

Reference + metric

  • Compared against an ECG chest strap (Polar H10 referenced).
  • Uses correlation/“agreement” plots, aiming for points close to the reference line.
  • Includes R value (correlation strength).

Indoor cycling

  • Overall: “looks okay,” but with noticeable errors (often too low heart rate).
  • R value: ~ 0.88 (“okayish”).
  • Several sessions showed issues:
    • Noisy at higher heart rates
    • Missed dips/peaks
    • One session appeared to have a time shift / data saving issue
  • Comparison context:
    • Mi Band 9 Pro ranks lower-middle, not top/middle tier.
    • It’s close to Mi Band 6 and Huawei Band 6.
    • Mi Band 9 (original) reportedly did a bit better in his earlier testing (different setup due to travel).
    • Budget alternatives mentioned as doing better: Huawei Band 9/10 and 8/9/10.

Running (outdoor)

  • Overall: correlation ~ 0.91 (not awful), but still shows systematic deviations.
  • Reviewer suspects cadence lock (locking onto running movement rhythm rather than true heart rate):
    • Deviations appear consistent with locking onto cadence/frequency.
  • Comparison context:
    • Overall ranking: middle; many devices perform better.
    • Even a budget Huawei Watch Fit 2 is said to do better.
    • Reviewer suspects Huawei Band 10 would do better too (couldn’t test due to injury).

Cycling (outdoor)

  • Overall: correlation drops to ~ 0.79 with “big clouds” of deviation.
  • Ride-by-ride:
    • Some rides look okay
    • Others are terrible (e.g., implausible HR spikes—around 180 bpm when he believed it couldn’t be correct)
  • Comparison context:
    • Mi Band 9 Pro is again middle (“not great but better than many”).
    • Zoomed in, it reaches “Garmin territory,” but:
      • Still not among the best
      • Mi Band 9 (original) reportedly did better in at least some conditions (testing conditions may differ)
    • For cheaper, reasonably accurate HR: Huawei Watch Fit 2 suggested.

Weightlifting (outdoor/strength)

  • Reviewer notes most watches struggle due to arm tension and difficulty detecting blood flow.
  • Overall: “seems to be doing okay,” but a familiar pattern appears:
    • In higher HR ranges, points are mostly below the reference → it can underestimate when tension increases.
  • Correlation: ~ 0.86, but many peaks are missed across sessions.
  • Verdict: Not good enough for weightlifting.
  • Comparison context:
    • Best mentioned: Apple Watch (upper-middle / potentially “good enough”), but with a downside:
      • Apple Watch tends to drop out (missing readings) rather than reporting incorrect HR.
    • Reviewer recommends ECG chest strap for weightlifting HR (most reliable).

Sleep stage tracking results (main findings)

Reference

  • Compared against an EEG headband (Zmax) designed to measure brain waves.
  • Sleep stages compared: Light, Deep, REM (“RAM sleep”).
  • “Awake” is ignored for performance focus.

Overall accuracy (percent agreements)

  • Deep sleep: ~ 68% of reference deep sleep detected as deep sleep.
  • Light sleep: ~ 43% agreement (confusion with other stages).
  • REM (“RAM”) sleep: ~ 27% agreement (worst by far)
    • Much REM time is mislabeled as light sleep
  • Awake time (for completeness): ~ 16% agreement (not treated as a key metric)

Pattern explanation

  • Reviewer suspects Mi Band detects too much deep sleep overall:
    • Deep segments overlap, but extra deep sleep is added.
  • For REM:
    • REM detection appears random and does not reflect expected sleep-cycle structure.
    • Total time in bed appears accurate, but sleep-stage breakdown is not trusted.

Comparison context (with other EEG-tested devices)

  • Mi Band 9 Pro is described as among the poorer performing watches for sleep stage tracking.
  • It’s close to Mi Band 9, with similar behavior to Huawei devices / other Mi Bands.
  • Huawei Band 10 is said to be slightly better for heart rate, but Mi Band 9 Pro’s sleep stage performance is not described as leading.
  • Best-performing sleep stage trackers mentioned:
    • Apple, plus Aura and Whoop (top tier)
  • For cheaper “decent” tracking:
    • Google/Fitbit devices (noted that they use a similar algorithm; older Fitbit models were referenced)
  • If spending more:
    • Pixel Watch 3 described as a good compromise for both HR and sleep stages.

Sleep GPS link

  • Reviewer argues Xiaomi likely uses the same sleep algorithm across Mi Band products, so Mi Band 9 Pro sleep tracking is basically identical to Mi Band 9.

GPS tracking results (main findings)

Test method

  • GPS quality tested by cycling the same route multiple times and checking how well tracks overlap.
  • Noted GPS tracks may jump through buildings when signal quality is poor.

Overall verdict

  • Acquisition speed: quite good (signal quickly acquired).
  • Signal quality: often jagged, inconsistent, sometimes deviates through buildings.
  • Tracks can be offset/jittery; some segments look bad enough to inflate or deflate distance.
  • Suggested improvements:
    • Better than no GPS
    • But performance is often worse than typical recent devices tested
    • Couldn’t find settings to improve satellites/multi-signal; left defaults on
  • Comparison advice:
    • Use a phone for GPS instead (phone GPS likely better for most users).
    • If Mi Band 9 Pro is chosen mainly for GPS, reviewer is not impressed.

User experience / “what you get”

The Mi Band 9 Pro is described as:

  • More “pro” in design and functionalities vs Mi Band 9 (because of GPS),
  • But not pro in health/sports tracking performance.
  • Users might still buy it if they like the Mi Fitness app and the device looks good.

Pros (unique positives mentioned)

  1. Built-in GPS, an upgrade over Mi Band 9.
  2. Deep sleep tracking is relatively better than other stages (~68% deep agreement).
  3. Quick GPS signal acquisition.
  4. Total time in bed / time asleep seems more believable than the sleep-stage breakdown.
  5. Attractive design / “pretty watch” (subjective).

Cons (unique negatives mentioned)

  1. Heart-rate tracking is often inaccurate, including:
    • Too low indoors
    • Suspected cadence lock during running
    • Large deviations outdoors (indoor performance is better than outdoor)
  2. Sleep stage tracking is weak beyond deep sleep:
    • Light sleep agreement ~43%
    • REM agreement ~27% and described as not following expected cycles
  3. GPS tracking is jagged and inconsistent, sometimes deviating through buildings, likely causing distance errors.
  4. Not recommended for weightlifting HR tracking; too many missed peaks.
  5. In budget comparisons, many alternatives (especially Huawei/Fitbit/older Fitbit) can do better for HR and/or sleep stages.

Overall comparisons made (high level)

  • Mi Band 9 Pro vs Mi Band 9
    • Pro: GPS added, better “pro” feel/design
    • Con: health tracking not improved enough; sleep stages said to be basically identical
  • Vs other HR trackers
    • Premium leaders: Apple Watch, Pixel Watch, and some Huawei devices
    • Budget alternatives: Huawei Watch Fit 2 and Huawei Band models (9/10/8/10 mentioned) outperform it for HR
  • Vs sleep stage trackers
    • Top tier: Apple, Aura, Whoop
    • Better affordable: Fitbit/Google ecosystem
    • Mi Band 9 Pro is near the bottom for sleep staging
  • Vs GPS expectations
    • Reviewer generally prefers phone GPS over Mi Band 9 Pro due to track issues

Unique points list (consolidated)

  • Systematic testing by a scientist; repeated the same protocol.
  • Faux leather strap vs rubber strap: no major differences noticed; limited time on rubber.
  • Heart rate tracking compared to ECG chest strap (Polar H10).
  • Indoor cycling HR: correlation 0.88; sometimes too low HR; noisy at high HR; missed dips/peaks; possible time-shift issue.
  • Indoor HR ranking: lower-middle; close to Mi Band 6 / Huawei Band 6; Mi Band 9 reportedly did slightly better previously.
  • Running HR: correlation 0.91; suspected cadence lock; some runs detected too high or too low HR.
  • Running ranking: middle; Huawei Watch Fit 2 and likely Huawei Band 10 better.
  • Cycling outside HR: correlation 0.79; big deviations; some implausible peaks; only general HR patterns may be okay.
  • Cycling outside ranking: middle; roughly “Garmin-like,” but not top; Mi Band 9 previously better in his context.
  • Weightlifting HR: correlation 0.86 but many missed peaks; not recommended; ECG strap recommended.
  • Sleep stages tracked: Light, Deep, REM, Awake.
  • Sleep reference: EEG Zmax headband; awake ignored for stage performance.
  • Sleep agreement:
    • Deep 68%
    • Light 43%
    • REM 27%
    • Awake 16% (for completeness)
  • Sleep stage error pattern: too much deep sleep, REM detection random/not cyclical.
  • Sleep stage ranking among tested devices: poor; close to Mi Band 9 and similar Mi/Huawei devices.
  • Sleep tracking likely uses the same algorithm across Mi products; Mi Band 9 Pro ≈ Mi Band 9.
  • GPS tracking:
    • Signal acquired quickly
    • Tracks often jagged, inconsistent, sometimes deviate through buildings
    • Likely distance over/under estimation
    • Hard to improve with settings; GPS not great
  • Recommendation logic:
    • If you care about health tracking: don’t choose Mi Band 9 Pro
    • If you care about looks/app: it may be worth it
    • For GPS: prefer phone

Verdict / recommendation

Overall: do not recommend the Mi Band 9 Pro if you care about accurate health/sports tracking. Heart rate tracking is inconsistent (especially outdoor and weightlifting), sleep stage tracking is weak for Light/REM, and GPS performance is not reliable due to jagged deviations.

If you mainly want an affordable wearable with a pleasing design and you like the Mi app, it might be acceptable—but for better HR and sleep staging, or trustworthy GPS, better alternatives exist (Fitbit/Google for sleep, Huawei for HR, phone GPS for navigation/metrics).

Speaker-specific views

  • Rob (single main speaker):
    • Emphasizes systematic, science-driven evaluation.
    • Focuses on quantitative performance vs references (ECG, EEG, GPS route overlap).
    • Overall skeptical conclusion: Mi Band 9 Pro is “pro” in design/GPS addition, not in health/sports accuracy.

Original video