Not perfect but I’ve been happy with mine (AM6B+).
I think Blu-ray java menus should work with the BD-j add on. I tested a basic looking 4K BD-j menu recently and that worked fine.
No Dolby Vision when playing full disc .ISO (.iso play perfectly but in HDR)
No AV1 hardware decoding, might play 1080p but won’t play 4K AV1 files.
Last time I tried CE played VC-1 but Android didn’t.
Also there is the matter of the TV-LED not working correctly with Amlogic SoC’s, there is a thread if you want to discuss this.