I found them to be great for when I was in the cutting up stage. I really like them if I am dieting down, and I want to develop maximum peak in the muscle. There not very effective for "building up," however.....too many reps.
You probably already know this but the utmost important thing for bicep developement in general is proper form; no back movement, and although you bend the elbows, try not to move the elbows back and forth. And....nice and slow! (at least for most sets) I know it seems like I am stating the obvious, but MOST people say they know these things, yet don't train their bi's with good form. This is just what I noticed at the many gyms I have attended.
Side note: I used to train for amatur body building competitions, and I used to also personally train people. I usually don't comment on "work-out" questions on forums, however, because I feel as if my opinion gets drowned out by the slew of other opinions, which are usually wrong (and I don't want to be the one to have to tell them that).
I always liked your input on MT, though, so I responded; however I might not of if it was someone else.

Take that as a compliment...but I would listen to "work-out" advise here very sparringly.
My $0.02 :asian: