Haven't tried this particular shell, however I use LiteStep and I've also had good experiences with bblean.
It's hard to notice any significant difference in computer performance these days, since I have a decent system, but before, on an older system, an alternative shell definitely was lighter on the resources for me. The changes should be easily reversed, at least they are with LiteStep (which is Open Source), and so I suppose a commercial product like AstonShell will be just as easy as uninstalling any software.
I'd be interested in knowing if anyone here have tried AstonShell too. Not that'd even consider switching, since LiteStep is free and Aston isn't (well except today that is) and I've grown to accustomed to the freedom of LiteStep. LS might be a bit hard to get going (text based configuration), but I certainly think it's worth it