Reading up on these and was wondering a couple of things
1) Are they as accurate as a regular barrel that is fully fitted by a smith.
2) Is there substantial cost savings ?
#1.. that really depends on the condition and alignment of your action. If true (many new ones are excellent, many recent old are meh), then it works great.... But if the action is wonky and needs to be blueprinted, then the cost advantage of the Remage is lost.
#2 Yes, the cost of a remage can be as little as 1/2 the cost of a gunsmith install.
Accuracy, if the action lock up is square and solid, then the target will not know if the headspace was controlled by a nut or shoulder.... at least to the 1/4 MOA range.
Ideally, you would choose an action designed for barrel nut prefit match barrels. Depending on your end goals, Savage or the Rem 783 would be my choices in the factory donor world. There are an ever growing list of custom actions that can support barrel nut prefits. I could offer you a Deadline.
If you were building a varminting rifle and want to use a Rem 700 and a Remage prefit, go for it. I have had alot of positive feedback from customers with this end use goal.
But for competition, I would start with a review of the receiver and decide from there.
Jerry