I recently put a new Criterion barrel on a Garand. I had some ambivalence about the break in routine, but I decided there wasn't a reason not to do it. On a week day, I typically have the local range to myself. On the day that I happened to pick, there was a top tear competitor (non break in believer) acquaintance, who is sort of a contrarian by nature. As I was shooting one round, cleaning, repeating, he was giving me a full ration.

Perhaps it's one thing for a sub MOA target rifle, and completely different (as Monty Python was wont to say) for a "Greatest Battle Implement".
I felt a little better a couple of days later, when I ran into a Smith acquaintance at the cigar bar, who opined that break in is legit, on a micro finish level, predominately in the throat.
As soon as I hit that lotto, I'm going to buy two identical barrels and see if it really makes a difference.