Hmmm... Break in? No baffles or such in a header, so not long at all. I did have to heat cycle the cat twice to get the bolts tight enough it didn't leak a bit. Other than that, I don't think there's a break-in period.
The JR headers are on sale about 2 months out of 3 for $429. It's already ceramic coated and it weighs less than the RB. The performance gains of the RB are small, and you can't bolt a supercharger on top of it.
And with the new shiny ceramic coating on the JR... it even looks as good or better than the RB. Sweeeet!