Don't get the topeak, it's a piece of junk. Well at least mine wasn't strong enough to handle the weight I put on it and it snapped mid ride. Pretty scary as at the time I was in traffic going down a hill at a decent clip with 40 lbs of groceries on my rear rack.

The stem that looks like metal connecting the extender piece to the part the clamps on to your bars looks like it's metal, but is just chromed plastic. I had my air zound horn (not the bottle just the horn), my computer (cata strada cadence wired) and my light (a 2 AA cateye model) on it, so maybe that was too much weight.

I've thought about going with the bdop, but I've just dropped a lot on other mods to my bike, so that's waiting for maybe next month.