There are not many locks that I would trust and they are expensive. I currently have a Kryptonite U lock and a Kryptonite hawser. I lock the frame- rear wheel and what I am locking to together- and if possible the front wheel is taken off and also put in the U Lock. The hawser will the lock the saddle and all of the bike to the lamp post or Bike rack. I would trust this lock for about 5 minutes to a determined thief.

But the dual lock system--- I see this used a lot in Brighton (Plenty of students and bikes there) The theory is that it is easier to break one lock than two so the thieves move onto an easier to steal bike. But if the bike is what the thieves want-- it is going to go.