FluidFilm uses the Fluidmotion rendering algorithm from Avid’s high-end motion effects engine, Timewarp. Fluidmotion also is used in other aspects of Avid’s higher-end effects, including motion-tracking, among others.
FluidFilm–without knowing too many details about it–simply converts interlaced footage to true progressive-frame footage. It’s pretty cool. If that’s all you need to do–convert interlaced footage to progressive, go with Avid and forget the Magic Bullet product.
However, Magic Bullet offers more than conversion. It features all sorts of looks and effects, damage, and other goodies. FluidFilm only includes conversion, no looks. For that, get Magic Bullet Editors AVX.
If you’re happy with Vegas, stick with it…FluidFilm is no reason to switch to Avid just for that in itself. However, since Avid is arguably the best NLE on the market, you should upgrade to XPro if you want the WHOLE AVID PACKAGE and not just a feature or 2. Avid also has better 3rd-party support (plugin effects, etc.) than Vegas, though Avid’s audio editing capabilities are pathetic…PALING in comparison with Vegas.
Just some things to chew on. Good luck with your decision.