A suspension seat post will bottom out after a while. To get the suspension back, you have to get off the saddle and allow the suspension to go back up. The Thudbuster has a much better system where you can set it so that it doesn't bottom out.

A Brooks Champion Flyer will cause you to bounce more than a suspension seat post. It's effective because unless you're real heavy, the springs won't bottom out. The saddle itself is hard and some people don't like it but overall, a very effective system. Once the saddle breaks in, you'll feel much more comfort.