I was speaking to a guy at Campaign from ReBall about them at quite some length. They perform really impressively, fly very straight and can be used about 5000 times apparently. He explained that although the price is high, once you have used them about 5 or so times they have paid for themselves. Also he said that with the soft 'rental' balls the gun needs to be chronoed at about 230-240 for the optimum flight path (and so it's within UK laws). I got a few samples to test out and i am very pleased with the results, I even tried them out by getting someone to shoot me with them. The gun was chronoed at about 290 with paint that was a good fit to the barrel, the ReBalls are a bit on the small side so they were probably coming out at around 260 ish. I was shot from about 20 yards or so and it struck me on the man boob area. I won't say it didn't hurt but no more than a regular paintball, the bruise went within a week. One thing that I did notice as the ball came hurtling toward me was that they seem to make a rather different (and cool) sound to regular paintballs, i thought it was kinda cool... before i squealed like a girl.