i'm guessing you have to know how to use them first.
I *THINK* the idea behind them is to force blood into the penis using you PC/BS(whatever) muscles, then clamp it, as you gain an erection, your dick will already have blood in it so it will be less painful.
Overall i think all it helps with is hardness in the upper parts of the penis(head, glans).
Well, just my 2C.