I've got a XR3 that I bought new years ago. It's a pretty decent low end regulator. You'll find lots of folks here bash Sea Elite equipment, but you'll see lots of bashing of other brands too. Some of their stuff I'm not real fond of, but as a basic low end regulator this one isn't bad. I've done at least 20 dives on it and never had any problems with it. Most of those dives were 40 to 65 feet I'd guess. But I've dove it in the 70-80 feet and not noticed any difficultly breathing with is.
One of the issues with this regulator thoug is that you won't be able to get service kits for it at your local dive shop. You'll have to send it back to Divers Supply for service as this is their "store brand". I've had my LDS service mine before, but they weren't able to replace all the parts in it and had to just "inspect them for wear". Luckily none of them needed replaced that they didn't have. They actually said it was built a lot better than they expected it to be.
As for the depth issue performance, it's a piston 1st stage I think so you might see slightly more breathing resistance at depth, but I believe that is a "feature" of the piston first stages. However, it's shouldn't be enough to generate a concern over.
that help some?
