I love the gun! Most of the negative reviews seem to be from people expecing an arcade-quality and weight gun for $30 (note that a Happ gun assembly is $120). Yes, it's made of plastic, and looks like a toy gun, not a 44 magnum. Yes, it's only one player. But it's rapidly become the most popular part of my cabinet!
It doesn't have autofire, so those games like Operation Wolf and Maximum Force where you may at times have a machine gun will require you to pull the trigger for each shot. In addition, the extra button doesn't aim, so for games like Operation Wolf where the extra button is a weapon, you have to pull the main trigger to aim then quickly press the second button to fire the extra weapon.
In addition, the stock version of MAME requires you to shoot the very last row ofpixels to reload in Area 51 and Maximum Force; there is a patch out to fix this, and it works great, allowing you to shoot offscreen to reload.
I just got House of the Dead 2 last night, and it plays just like the arcade! (Note: It's buttons aren't remappable... make sure there's a button on your cab mapped to Enter, which it uses as P1 Start!)
Two guns would make this perfect, and u_rebelscum is working on it in MAME Analog+.
--Chris