I've seen the infomercial on tv for the cat emery board and it literally looks like a giant emery board stuck on a curved piece of plastic. I really don't think a bun would use it. If they even do bother with it, I doubt it'd be enough to wear down their nails sufficiently. I don't know about other bunnies but mine certainly grow tired of "toys" very, very quickly.
Clipping nails on my own is a good use of time to inspect the bunny all over, about once a month, to make sure I haven't missed something funky happening on their bodies.