With 98% to 99% efficiency, our shaft drives bikes perform more consistently than chain and derailleur bikes that range in efficiency from 75% for poorly tuned systems up to 97% for perfectly tuned systems. - from website
Sounds interesting but probably needs more time to mature. I think Shimano just came out with a new 8 speed nexus hub. Tinkering with the drive train looks like it would be much more complicated, but on the other hand it shouldnt need as much service.