As only a small fraction of the games really use STE features, an STFM is not that bad.
Compatibility is another issue but I suppose that most of the normal ST games work properly on an STE.
As STEs are rare, finding a cheap STFM would be a nice solution. You could even buy a cheap STFM first and use it until you find an STE. Having two Ataris at your disposal is often a nice thing as well.
