First off, welcome to the ASAZ forums. You've certainly come to the right forum, as I know just about everything there is to know about this gun
. I bought it back in late August and have used in multiple airsoft wars since then, as well as plenty of target practice, and this gun continues to satisfy with every shot and every kill.
I don't have any personal experience with WE GBBs, but I can tell you the paint finish (save for the orange tip) on this gun is one of the best. I've had this thing swinging around in my holster, clambering over trenches in the rough desert terrain while it's in hand, all kinds of things, and the paint remains completely flawless, save for one tiny chip in the orange tip, and the expected wear in the back of the gun where the hammer hits with each shot.
As far as comparing it to the TM MEU, The KJW MEU (or KP07, as it is also known) is actually far superior to the Marui, for a fraction of the price. It features an enhanced red loading nozzle, as this gun is able to use Co2 as a power source as well as green gas. I'm not 100% sure if it's compatible with Marui parts, but even if it's not, KJW parts are widely available, most of which you can now get on AirsoftGI.com. You are correct however, on KJW's incompatibility with WE parts.
Now onto performance.... This gun will hit distances of up to 100 feet with exceptional accuracy, and even up to 120 feet accurately with Co2. The main difference between green gas and Co2 is power. The gun kicks harder, shoots farther, and at a higher FPS with Co2, though green gas is still a very adequate power source. I can get about one full mag's worth of shots (give or take about 5 or so shots), which is 26 rounds, out of one fill of green gas. With Co2, however, I can get between 2.5 and 3 full mag's worth of shots (give or take 5-10 rounds) before needing to replace the Co2 cartridge. FPS is 330 with green gas as chrono'd by ASGI when I bought it, and Co2 is said to chrono around 350, which seems accurate based on my experience with the gun. Also, this thing is loud and can be intimidating. I've had friends with high end AEGs literally dancing their way to cover while running away from me with this thing. Ahh, good times.
The biggest letdown on the KP07 is the fact that the barrel is not threaded; therefore, you will not be able to attach a silencer. As far as any other issues.... When I first bought it, the Co2 mag's gas release pin and spring behind it kept popping out when firing the gun. After this happened on several occasions, and I put it back each time, the problem somehow fixed itself, and it works perfectly now. I should also note that everything else, including the green gas magazine, has performed flawlessly since day one. Let me also say that this gun is no lightweight; it is made entirely of metal, and weighs in at around 4 pounds (maybe a little more) with a fully loaded magazine. Great weight in your hands, and is balanced perfectly throughout the gun, however if you plan on running around the field with it holstered, particularly on a leg/thigh holster (as I do), be prepared for a bit of an adjustment period, as you will definitely notice the extra weight.
Overall, I really can't say enough good things about this gun. It feels extremely comfortable in your hands (especially with the rubberized grip), white painted front and rear (and adjustable!) sights work perfectly, mag capacity is great, cyclic rate is amazing (fires as fast as I can pull the trigger), accuracy is great with .20g BBs, power is ideal, and it is just plain fun to shoot, be it in a game or in your backyard. Everyone I show it to who hasn't already seen it is always impressed by both its aesthetics and performance. Best place to buy it is AirsoftGI, as they give you two magazines (one green gas and one Co2), as well as optional free shipping, and from now till 1/3/2011 they're doing a promo for 10% off your entire order. Even without the promo, $125 for this top quality gun and TWO magazines really is an unbeatable price!
So, does that about cover it for ya?
If you have any more questions about the KJW KP07 1911 MEU GBB pistol (it's full name), please don't hesitate to ask.