All right, finally had a chance to try out the McCuff...and promptly wound up with gas squirting up onto my seat and the inner lid of the plastic that goes over the gas tank. It happened right as the fuel clicked off--yet the tank wasn't quite full--so I'm not sure it it was the McCuff, or if I moved my hand and broke the seal.

I'm kind of leaning towards the latter. I'll fill up again in a few days and see. If it happens again, I'll probably not use it. What's the point?