Can't change barrel, so must use standard bore paint.
I used this gun for a full set of games. Went through around 1000 balls in probably 20-30 games. It's got a few quirks but once you get the feel for the pump stroke, the action is fast and reliable. On the other hand, I found that if you use bad pump technique, you can get double feeds, misfeeds, balls broken in the gun, etc.
Accuracy is reasonable. It's probably not the absolute best in terms of guns out there, but it's not that bad either.
Personally I like the minimalist design of this gun. A lot of modern pumps seem over-designed to me: regulators, stacked tubes, double triggers, etc.
I don't know if it's possible to rig something up to drop in an aftermarket barrel.
I'd get this gun if you're looking for a reliable, solid pump gun. The only real downside is that you are stuck with the standard barrel. Not a big deal unless your preferred paint is some non-standard bore.