I own a MIDI Fighter and I use it for both DJing and with mGB and an Arduinoboy for banging out drum stuff for some projects I am working on. I'll weigh in:
Get the Spectra, don't buy an older MIDI Fighter (unless it's the MIDI Fighter Pro, which is a cool and rare beast) secondhand. The 3D one (in my opinion) is nice but unnecessary when it comes to the motion sensitivity thing. The big thing is platform/software compatibility. If you want to use it in Ableton, you'll have lots of fun using it in the drum rack. Be sure to check out Mad Zach's tutorials for custom drum rack building. Make sure you think carefully about the button designs on the unit itself, etc, they are hard to re-arrange.
Be aware that the buttons are not pressure-sensitive, so you may have to manually go back and add velocity/sensitivity to a lot of drum stuff. I use the pitch bend wheel on my MIDI keyboard to map the velocity while drumming with one hand, it allows me to accent by wheeling up and decrease the intensity of certain notes/beats, and the pitch wheel snaps back into place, which is handy.
However you use it, make sure your hardware or software will compliment its limited yet powerful mapping. It's tons of fun, makes drum beat and note entry a snap. Great to throw in a bag, or DJ with at parties. Also, the resell market for these are pretty solid (if you have a symmetrical/tasteful button layout) and you won't hit a mega-loss financially if you decide the MIDI Fighter isn't for you. PM me if you have any questions or need any help setting up. 
Last edited by thebitman (Aug 20, 2013 9:00 pm)
