Welcome 34fun,
I'm not really up on H&R shotguns, but I believe the USH is on a 10 ga. frame which rifle barrels will not fit, and the slug barrel won't fit a rifle frame. If I'm wrong, someone will come and correct me........make me stand in the corner with a dunce cap. As far as quality is concerned, most of us feel it's at an all time high. Brian56 is one of the fine H&R gunsmiths and a member here. He makes sure everything gets done properly. If there is ever a problem. Brian jumps in to get it corrected......like right now. Many of us have happily used the accessory barrel program. Turnaround time is down to about 2 - 3 weeks, including transit time, from 6 - 10. Five or six of my Handis were born in the barrel program. All of mine are complete rifles today. Read the FAQs above. It'll tell you all you need to know, and then some. You can buy barrels in the classifieds here, and fit them yourself.
Good luck,
Pete