I dunno from nuthin' about a bushmaster.
When they first invented button rifling, it was supposed to provide sharper cuts and more uniform lands and grooves than conventional.
Cynical old me, it seems that polygonal rifling is a way of charging more money for a gun.
Unless you're heavy into benchrest or match competition, I wouldn't worry about it. I bought a JC Higgins .270 back in 1964 (conventional rifling) which shot about as good as most anything else I've ever owned.
I guess my 1970 German-made Weatherby '06 is hammer-forged; it shoots good. My 1970-ish Sako shoots good, but I couldn't tell you is it conventional or button.
Hey, they're in business to sell guns, aren't they? Americans like gimmicks, whatzits and whichits, don't they?
FWIW, the Ol' Fart