That's not a worm gear drive, which would only be about 30 to 50% efficient. It's a bevel gear, similar to what's in the rear end of a car. These can have pretty good efficiency, in the range of 80 to 90%. Amount of power? They claim 200watts. This makes it a power assist device; not a motorcycle for sure. Still, a useful amount of power. If I could put out 200watts and this can add 200 watts, together we would be about 1/2 a Lance.
At least for about an hour.
The nice thing I see here is the weight. With the LIon battery this whole package is 1900g. That's only about 4.2 lbs. That and the inclusion of the freewheel in the drive so if you are spinning the cranks yourself you are not fighting friction from the motor.
Someone else mentioned it would be better if the power could be applied to a IGH. Well it is. The motor spins the crank and the chain will spin through what ever gear system you got on the bike. Internal geared hub, or standard DR system.
There are two things not so good:
1) When the motor is spinning the crank, you better be clipped in or very carefull not to let your foot slip off the pedal. They are spinning under power and your feet are going to have to keep up; or get bashed.
2) I haven't been able to find a price for this thing. Any body else find a price listed anywhere, or place where you can actually buy this?
OOPS! I just went back and read the article on the OP link. I see $2400 is a little steep.