The Masterlock Streetcuff takes a novel approach to the bike security problem. Using a hardened laminated steel construction, each cuff has an internal diameter of 3in - enough to lock the front wheel to the down tube using both cuffs, but not the rear wheel to the frame using just one.
Under attack, the cuff holds up incredibly well. Levering isn't an option as there's little space to get a lever in, and under a manual attack of up to five minutes, these didn't give an inch. However, with the power tools out, the cuff finally relented after a pretty impressive four minutes and 30 seconds.
The cuff is a unique idea and suited for use on road bikes. However, it's not practical to use on its own to secure a mountain bike (but is great for securing the front wheel to the frame).