BB7s are not difficult to set up...but they are exceptionally sensitive to proper setup. A lot of rim brakes will work great when hastily rigged up "just close enough", which is about what you get from a lot of bike shop employees.

As far as performance; I have BB7s on one of my bikes. In dry weather, they perform exactly the same as the Force calipers on my road bike, or as the Shimano cantis on my crosser. I'm sure there are differences, but without applying quantitative rigor I can't subjectively tell the difference.

In wet weather, those BB7s shine. The other brakes noticeably lose effectiveness, while the BB7s work exactly the same, albeit with some squealing on the wet rotors.