The only advantage this has is to replace GBB sidearms and shotguns, really. The velocity isn't anything to shout about according to that page, and neither is the 4 rounds a second. It wouldn't effect rifles since they gun off rechargeable batteries anyway, plus it said it was a pump-action only mechanism. Its too much trouble to go to just so you can say "my gun is one step closer to the real thing."
If it really costs the $700 quoted earlier to make this, you can go buy a real gun!