1) Yup... M4 plus accessories is expensive as hell.
2) That button makes slug select/de-select and "cruiser ready" super fast and easy.
3) I don't find it to be that heavy, but then again I'm not going to be carrying it all day across the tundra.
4) My M4 eats everything I've tried to feed it, from the cheap WalMart aluminum head #8's up to some monster Brenneke slugs.