Most, if not all, themes are compatible with shapeshifter and themechanger. The difference is that shapeshifter doesn't modify key system files that can f**k up your system, while themechanger does. For the amount of $ that unsanity wants for shapeshifter, I'll pick that over spending hours reinstalling and recovering my system and getting it back to the way it was before. Anyone who would choose modifying core system files when another choice is available is, as others have already said, a moron. Or a jealous developer.
Second, all of Max's themes are free and he only asks for donations. Some of his themes are original, some are improvements of existing themes, and some are even ugly. But that's the nice thing about choice, people's tastes, and free enterprise. Max is one of the fines themers I've ever come across, and having the opportunity to change the look of my OS, even for a little while, is absolutely refreshing. Keep up the good work, Max! A lot of us look forward to every new release you come out with!