http://commutebybike.com/2006/04/09/street-cuffs-snap/
They look very weak. You live in NYC? I would not use them. If you're looking to save weight you might consider OnGuard Mini Bulldog TC, it's about 2lbs, inexpensive, and fairly close to the security of the Krypto minis. They both resist leverage attacks due to their size and I think may require power tools to defeat. Using the sheldon method you just need to go through the rear wheel inside the rear triangle (grabbing the frame can't hurt either if there's room). Use a 2nd one for your front wheel, or use a separate locking cable for it + frame + rack. That way the crook would have to cut 2 kinds of locks to get the bike. i see no need to have a cable running between 2 u-locks.