Um.

Looks like a huge opportunity to break something in your drivetrain. And I can't see it being all that much quicker than a ulock. And on my bike it would be WAY the heck dirtier (my drivetrain is NOT clean).

Also I'm a bit skeptical of your claim that it won't let a fixed gear be walked. I suspect it would just go around the chainring while doing damage to the lock or the chain or both.