I got the MCC-216, and Amiga compatibility is not that great. The most annoying problem I found is that the Workbench does not work, it will freeze when accessing disk from desktop.
The compatibility with C64 and Atari 2600 is a hit and miss, you wont know if it works until you try, and also there is some weird bug in the keyboard code in C64 mode that prevents you from typing * and types a different character.
The Spectrum core seems to work fine, but most games don't support joysticks, so you need to play using the keyboard and I'm not a fan of that.
