In reply to d80f0u:
I like the title of your thread, straight to the point.
I use two Jokers whilst guiding and belaying, for this I use a Reverso3; it works fine. As you would expect the Joker is quite slick anyway, but there is still a fair deal of control to be had.
Actually, I was out on a multi-pitch this evening, and ended up abbing on a single Joker, it was alright and even though I had backed it up with a prussic I still felt safe and in control.