search, there was a thread not to long ago that Klif was talking about the same thing (double beadlocks)...couple points is WHY, and brake caliper clearance. the thread had some good points but I am too lazy to find it right now :-\
yes, but they are an internal lock...looking at the wheel you would never know if it was locked or not, they are a two piece design and have either a runflat or a PVC insert that go inside the wheel and presses the two beads against the rim, and locking it on...