The KWC Uzi is the one to go for. Co2 and BB's together, so mag changes are quick. The mix of plasic and metal is well done and the all up weight is a hefty 2.2kg, loaded. If you tuck the wire folding stock against your cheek, - your fillings aren't going to last long! I get 2x mags of 20BB's per CO2 bulb.

There are a few things that need work to get the best from it. 1/The grip safety needs a shim at the bottom, unless you have huge hands, otherwise it either it needs an ultra tight grip or held as high up the grip as you can get.2/ The sliding safety has 2 detents on a strip that are far too high and the holes in the sliding bar are not chamfered - resulting in a very stiff safety slider. After sorting those out it slides easily and smoothly.3/ The Uzi doesnt have a "hold open on empty" - But I got an idea for that. It's quite an important omission on the KWC Uzi -as there is only just enough gas for 2x mags - If you overshoot on the fist mag, there isn't enough left to finish the second.
Also, as someone pointed out earlier, there are spares for KWC BB guns - unlike many of the other brands. So if you want to do the silencer thing, you can get a spare barrel nut and pin it to an airsoft silencer. Another mod is to turn down about 1.5mm of the foresight post and attach a red or white sleeve to the tip of the pin for shooting in low light.

Have to agree about the Umarex plastic C96/M712 being more reliable. I modded mine with a Box shoulder stock/holster and harness. I did a bit of paint and polish on it too - just to make it look a bit less plastic. It is fast and accurate and has worked flawlessly. It's also great for trolling your shooting mates in a BB pistol shooting comp