Wood is a little different. Handgrips and buttstocks have to match the frame. In other words it has to be a G2 buttstock on a G2, a traditional Contender on a Contender. Forends will interchange in most cases. I had to trim the ears on one but I can't recall which one to get it to fit one of my G2s.
I like them because most stuff fits most stuff, and if it doesn't work completely (bolts needing to be stoned or minor mods to wood) it isn't a big trick to make things fit. The exception being the muzzleloader for the G2, and having never seen one I can't comment on how that one doesn't work. I just know TC says it doesn't.