A few people here have had Dynamics in the past and have posted that the drive is not that great. It's not efficient, the shaft can tend to torque giving a springy feel to the drive, and the bevel gears break much more easily than chains.

You can't use the lightest weight and most efficient transmission ever devised, the rear derailleur, so if you want gears, you have to use an internal hub, which adds even more inefficiency and another pound or two of weight.

Also, changing a flat tire on it is said to be a chrome plated pain in the rear.

Their claim for "simpler to maintain" is correct in a way. You don't have to do frequent service, no chain oiling every weekend, etc. You just have to buy and bolt on a whole new shaft assembly every 8000 miles or so, at I'm sure many times the price of a new chain every 5K or so.

Apparently the primary market for Dynamic bicycles is beach resort cruiser rentals, where an enclosed drive train that can't get grease on your clothes is more important than efficiency, and rebuilding the drivetrain every year or two in the off season for 50 bikes isn't a big deal.

If there's a "future" that doesn't involve a standard chain drive, I'd bet on belt before shaft.

At Henry Ford Village (part of Henry Ford Museum) in Dearborn, MI, they have Orville and Wilbur Wright's bicycle shop where they built the Wright Flyer - the actual shop, they moved it there (along with some buildings from Menlo Park). One of the things they have in there is a shaft drive bike from the 1890s. The actor's script goes on about how this is some kind of miracle thing that is clearly better than what we use now and just is waiting to be rediscovered. After he finished and people were going through, I approached him and said I knew he was just doing his job, but people do make shaft drive bicycles today, and there's a real good reason why they don't sell very well.