Hi!
I have been using a Joby SLR Zoom for a while. Yes, it can grip and hold on to bars and railings as in the picture. However, it tends to slip if you are not careful- so it takes some effort to really twist the legs around well. It can also be tricky to frame the shot, as you are dependent on the fixed support railing. I mount a manfrotto 484 on it, so I would grip the legs tight, then use the ballhead to frame. Its easier this way.
You cant move about to position a good location like a regular tripod. I am not sure if in the long run the joints will loosen up, but if you want a simple holiday tripod, this is really convenient.
Hope this helps.