The things are about the funnest pistol you will ever fire in your life. I have fired my neighbors on two different ocassions and I loved it! He had a .50 AE Brushed Chrome Model that was extremly fun to shoot. I have never had that much fun shooting a pistol in my life. One other time I fired a .50 AE in the regular blued model that somone had at the local indoor range. The thing is an absolute beast and the flame that erupts from the muzzle is like a fire breathing dragon. When you tap off a round the entire range immediatly STOPS.
Then about one second later, you tap off another round. It sends a shockwave down the entire group at the range. Everyone there is drawn towards the gun. I can guarantee that you will get some looks if you go the range with it. Everyone I have have ever been around while fireing the weapon was amazed. It is really a cool piece.
After firing about 20 rounds and you sit back down to your little .40 S&W USP it feels like a little pea shooter.
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In my opinion they are a novelty gun. Serves little use outside of the shooting range, although my neighbor keeps his .50 AE loaded on his nightstand. They are alot like tricked out AR-15's, serves little pratical purpose, but the dang things sure are fun to shoot.
As for reliablity, the one I shot worked great. The only problem was that I teneded to go with the recoil and the slide wouldn't cycle the next round. IF you kept your elbows locked it worked 100%. Great gun.
(You could also use them for deer hunting.)
Good luck!