Stupid me (*slaps himself*)...
A Y-Pout style spinner would have the problem in that you cant just decide you want to go forward, and go forward. You wouldnt be able to move in any forcefulway (trying to push someone) from a standing start as, if the motors are high rpm, thus less torque (Ed put awy the lem )then it would take a good 3-4 seconds to get to any good speed.
Then again they may have more advantages than disadvatages. But seeing as I may be getting some sponsorship from a Bristol-Based CNC company... Id like to go the walking route to a MAJOR featherweight spinner.