Really, just wanted for the Amiga side of things. I still have my 64 stuff so really no need to emulate that at this time, even know the MMC-216. I mainly got it because it was suppose to emulate the Amiga and the Atari 2600. 2600 emulation is fine. But the Amiga one is still in beta.
If you want better adf-compatibility *now*, then go ahead and buy a Minimig. Otherwise, I would at least wait for the first non-beta Amiga core for the MCC-216 which might get released soon. Nevertheless, there is quite a number of games which are working:
http://www.retrorebooted.com/mcc/forum/viewtopic.php?f=5&t=4Regarding the current Atari 2600 core, my experiences are not that good. There are quite a number of games with issues. Also the video output seems to be non-standard sometimes and my display fails to sync in a few cases while it always does using the C64 and Amiga core.
