Basically I think it works fine.
Sometimes changing from one app to another takes a few seconds, but I think that was also the case on my former X II installed on A11.
For my simple usage (phone, SMS/MMS, camera, alarm, notes and web browser) the only problem I have is that the bluetooth isn’t working well in my car’s handsfree system (VW) – I can hear the others, but they don’t hear me. That worked OK on the previous phone.
The web browser basically also seems to be working OK – I don’t say “up to speed”, but mostly quick enough for my usage. (What really irritates me is that some sites responds that the browser is too old and not supported for advanced funcitions - but don’t know if that would have been better on A11, probably not.)