You should be aware that Mini-Mig is an Amiga chipset interpretation
It will contain bugs. Compatibility will be high, of a similar level to WinUAE (one of the sources of information upon which Mini-Mig was based.) but it will not be 100%
A Mac Mini running WinUAE is small
Probably smaller form factor than 15cm x 15cm and it has other uses other than WinUAE.