I'm using the UPR o/r x-pipe in my Venom kit. The quality and craftsmenship is okay. Not a big deal, but I found a piece of weld wire in mine. I have the Dynomax 3" catback instead of the Flowmasters. Sounds pretty wicked IMO. Gave me about 12 RWHP and 15 RWTQ increase over the stock H-pipe.
Definitely louder, but not a lot like most people seem to think. At least not with me. The dynomax mufflers are a straight-through design, similar to the magnaflows...