Button rifling is fine for an AR or other type of barrel that isn't going to be used for SERIOUS competition.
Essentially you take a piece of steel that will be your barrel and you under drill a "pilot hole" that will be the bore. Than you take a "button", which is like a rifled slug for a shotgun, but made of seriously hard steel and you FORCE it down the inner steel "pilot hole" of the barrel with tremendous pressure. As the button goes, it rotates and "cuts" lands and grooves into the steel, thus making a 'barrel' out of it.
mjkeat hit on another couple of interesting questions, but given their answers to the basic questions you asked, I would say their A-ok.
15,000 round count life is most likely out of their chrome lined barrels, which is fine, but you don't need chrome lining unless you are going to be shooting thousands of rounds in short order.
A basic chrome moly barrel would do you fine for your application and with their guarantee, I would say you are good to go.