I updated to Oreo and performed a full factory reset after the upgrade. I'm happy with the new interface and my Mi Box is working well. Just my personal experience. Either way, enjoy the new Mi Box.

I actually had more bugs on Marshmallow and they were fixed on Oreo (like wifi disconnecting randomly). It did introduce new bugs for some users, and some bugs that were present on Marshmallow are still on Oreo. They released an update recently that should fix some of the bugs introduced in Oreo.

I would recommend to update, and even if you did it would probably be updated automatically the next time you reboot. The worst bug for me right now is sometimes (like 1 in 15 times?) it won't wake up from sleep when you press the "on/off" button on the remote, but for some weird reason clicking the "back" button repeatedly does seem to wake it up.

You can't stop it. Might as well go with the flow.

i'd wait a little. there are quite a few bugs that affect a certain amount of people. i think it's a lot to do with older televisions and routers but YMMV. chances are you will probably be fine but knowing xiaomi is working on those bugs, might as well wait so your device isn't messed up while you wait for the fixes.

I would wait till Xiaomi publically release a WiFi Firmware fixed update. That is a must have reliable thing that you need working, it's currently unreliable with Oreo.

Also Oreo will break all Audio passthrough, no matter what App. Netflix video playback is also pretty choppy with Oreo vs the previous Marshmallow Firmware.

Updating killed most of my stuff because 5.1 audio doesn't work now.

Got mine 2 weeks back and the first thing i did was update to Oreo. I didn't even format post that. I haven't noticed any bugs which have hindered my usage case.
My setup is barebones and no high end audio or wifi thingy, etc. Youtube, Plex and Puffin browser for streams being the usual.

Satisfied so far.

After update my box bricked and remote stop work