I have one. Maybe 4000 rounds through it. Semiauto function flawless. Power very adjustable.(Like, 7 to 70 fpe.)
Like all pellet guns, it has favorite pellets. As near as I can tell, the key to accuracy with this gun is finding pellets that locate consistently in the revolving magazine. There is no probe, so the effective probed depth is the for/aft location of the pellet in the cylinder at firing. Most pellets fit loose enough to shift under recoil or tilting the gun nose up/nose down.The Beast is such an exact fit to the cylinder length it can't shift, and the wide skirts of RWS pellets engage the cylinder mouth snugly. These are known good pellets.
A lot of the barrel swapping stuff is about shooting slugs. Slugs through the factory choked barrel will work, but keep an eye out for fouling.
I've done great by Mrodair, but there's lots of unhappy campers out there. Look to importing from a european dealer if it makes you feel better.