Good question. I know I've read that some people prefer the one without cams. It is capable of a wider range of settings which can be useful if you're working with odd shaped or sized buttons. I think the only one I've actually used is a Greist(sp?) branded one that uses the cams. It produced nice looking buttonholes. You want to go twice around for a nice full stitch pattern. They're fun to watch anyway.
Rodney