Since it only takes a single finger to make a sound instead of a whole hand, the Drumitar gives him the ability to individually play the role of three drummers simultaneously.
Furthermore, since he records his own sounds and has more buttons on the instrument than he has fingers, he can easily play a large number of different sounds. This allows him to integrate diverse percussion styles in a way that a single musician could never do. It's an amazing instrument that really separates him from other drummers (some may say unfairly so, but it's cool with me).
I've found a few videos of Futureman explaining his unique instrument. The first is a very short and overly simplified explanation of the instrument, but the next two are from an 'interview/jam session' hosted and posted by James Ross where Futureman explains and demonstrates the amazing abilities of the drumitar. The last video is of the 'Zendrum', a commercialized drumitar that isn't as cool as Futureman's but available for you to purchase and try out on your own (for >$1k). Enjoy.