I like using an old inner tube wrapped around the top tube. And it's entirely functional. All it takes is one fool to knock your bike when it's locked up. My bike fell and it ground a strip of paint off the entire length of my top tube. This isn't going to do much against bar knock if you get tagged in traffic, but will protect against more cosmetic damage. Go Kashimax if you're really worried about dents. I got a solid dent when I went down last spring; wish I had a top tube protector.