I had one and really did not like it. With any kind of weight at all it would shift to one side or the other. Once when I went over a rough set of railroad tracks it bounced so badly that it knocked my fender out of alignment. Mine also didn't work well with panniers because there was nothing to attach the bottom of the pannier to, which meant that the pannier would swing away from the bike when I turned corners.

You might be able to make it work with a basket or milk crate if you don't carry much weight.