The primer carriers are a bit of a drawback in a way, but the good thing is they make it easy to tell if the rifle is potentially "live" and they last indefinitely. Just wash and allow todry after use. They are easy to use and make priming easy for old hands and eyes (or anyone else for that matter). PRBullet.com markets and .25 ACP breech plug that he might want to get later, but for now an extra package of carriers along with what is included with the barrel should be enough.
The carriersdo not limit blowback at all and the barrel cut where they fit allows blowback to be directed straight out. I've never heard anyone complain of that being a problem, even left-handers. They are also nota waterproofing enhancement.
The single biggest complaint aside from the ramrod (so far as I'm concerned) is the stupid breech plug tool H&R provides. It works but can be greatly improved. I suggest you check out this
THREADfor a world of info. One link is to
http://perkloafm.com/where he outlines tool improvement and other useful info.