This is the most accurate source of FW versions and downloads. Posts often include official OTA links. https://geekdoing.com/threads/xiaomi-mi-band-4-official-firmwares.1372/
You don't mention which Amazfit version exactly. Check the list of devices on Gadgetbridge home page. If your device is fully supported, then you don't need Mi Fit. Otherwise you need to install Mi Fit at least once, to register the device with Xiaomi servers and obtain the security code. Once you have the code, you can uninstall Mi Fit and use Gadgetbridge or Notify & Fitness for Amazfit.
Mi Fit apk doesn't contain FW files for MB4 anymore. They are downloaded from Xiaomi servers after pairing and connecting the band and only after Xiaomi server flags your band as eligible for an update - as with standard staged OTA updates of smartphones. On a rooted phone you can find them in /data folder of Mi Fit (folder Firmware with random file name for FW and RES, if I remember correctly). You can't obtain them directly without installed and configured Mi Fit. Geekdoing shares BIN and RES files, if you do not trust them, use OTA links which are sometimes provided as well (or keep installed Mi Fit on your phone for FW updates).
I find MB4 accurate enough, compared to MB2 it provides roughly the same stats. When I manually counted steps, MB4 was spot on. Pulse was about the same as when measured with digital blood pressure monitor. If your MB4 provides widely different results than MB3, you should consider applying for a warranty repair/replacement as there is no reason for it to differ.
N&F has much more features and customisation options than Mi Fit. Also it barely uses any CPU, which can't be said about Mi Fit.
I'm using 1 minute interval with automatic activity and sleep detection. Missing HR data happens to me during night occasionally, I suppose that it's because of how the band rests against the hand during sleep. Sometimes it probably gets into such position that HR can't be measured (or there is some bug in FW, though not sure why would it happen only during night). It doesn't matter which app I use as the data is missing on the band itself and it never happened during the day.
I suppose that intent in Gadgetbridge works as in Notify & Fitness. It gets updated only if band measures HR - you need to measure it manually from the band, from the app, run a workout or setup continuous/periodic HR measurement in Gadgetbridge. Receiving intent is passive action, you can't send any instructions to the band or other app. For active instructions you need to use events - in such case you can use your own app to "wakeup" Gadgebridge which will then instruct Mi Band to take a HR measurement.
I don't use this app, but you might have luck with following the official documentation (export, import and import with merge):
Thanks for this. I didn't realise they had their own site and defaulted to XDA
That page is exactly what I was looking for!
