Looks great, and the Jackhammer Reg is the best you can buy. The short-throw 4-way is sweet. I've heard a few complain about leaks and reliablility but I've never had a problem. I screwed it on, adjusted the timing and it's shot perfect ever since. Price is unbeatable for all the components and front block in one package. I have the LP version and it is very consistent.
Nothing so far.
Definitely worth the cost. Great in comparison with other manufacturers. I've heard lots of people with problems though, so maybe the quality varies unit to unit...