Mi Band 2 -> AW4 -> Mi Band 4 user here. So I think I can answer your question here.

Mi Bands
Compatibility -> 101% yes.
Stability -> 50-50. Why? Well, it sometimes only vibrates to tell me there's a notification eventhought I have set it to always ring me when there's one. (Whatsapp, SMS/iMessage, normal calls). Sometimes it can notify you but sometimes it just can't even when you can clearly see it's "connected" @ the Bluetooth settings.

AW
No need say. I was annoyed by the 100% uptime telling me there's a notification that you wanted and so I sold it and now start to miss it again. Aiming @ AW6 now.

For ur case, Mi Band is good for like SIMPLE activity tracking and 50/50 chance of it ringing you on notifications. HMU if you want to know more in depth!

Alarms -> Din try much but my parents have it. They claim to be reliable/on time. It vibrates.
Sleep tracking -> My Mi Band is 24/7 on my wrist. Haha. Recently not so accurate. I slept @ 12am wake up @ 7am, it says I slept @ 3am, woke up 5am. ????????? Side note, I bought this MiBand last year October (2019) and wearing it everyday ever since.

I miss the AW because of it's 100% notification reminder to me. With the MiBand, I easily lost the reliability on that. My phone's 8+ so I kinda hate to keep taking it out to see who/what texted me. Sometimes, I can feel it vibrate in my pocket but my MiBand doesn't inform/vibrate. + it actually made me feel a little motivated to go exercise as I can be lazy

TBH, I really wanted AW6 cos I saw the news where iOS14 has barcode scanner for Wallet and have the option of "Add Card" in Settings but it seems like Apple has turned it off. That's a bummer.

This post has been edited by PoisonSoul: Sep 1 2020, 04:31 PM

Erm, more accurate tracking? Well my main aim as per said was for Apple Wallet but things are not doing well rn.

Well, it's a better Spotify remote control.
Do note if you use Spotify, you cannot do anything except just as a remote control. Only Apple Music you can download the songs and stream it offline from the Watch directly.

Oh another, stability/reliability than the Mi Band in giving notifications.

This post has been edited by PoisonSoul: Sep 2 2020, 04:08 PM