(Thanks SoulScribe for banner)
I figure, that since I made a G&G one, I might as well make some more of these, and just write down my experiences with these guns.
I used a CA M15A4 TC almost all last summer. It was completely stock, only thing new in it was an m120 spring.
The CA guns used to be one of the top competitors, they were always the recommended brand for more than a year(if you didn't get a lemon), next to TM.
Although their externals are metal, they aren't always the highest quality metal. From what I found, you either do or don't have good CA externals. They are made from pot metal, so you never really know what you'll get.
Personally, the CA I used, has been played with in all sorts of conditions, and because of this the metal started to get small rust marks on it within the first two months. They aren't noticable from a distance, but they are there, and around the edges of the gun.
The internals of the CA are alright. Their gearboxes aren't put together to take anything you throw at it. The actual gearbox shell isn't the strongest out there, but it's not the weakest either. You can put a m120 in it and not have to worry during the summertime, but when it comes winter, you may want to downscale to a 110 or a 100. I personally wouldn't trust the gearbox not to crack.
I like the trigger system in the CA guns, it's nicely put together and easy to put in and out. I haven't had any problems with the wiring yet, it's not bad, but I'm sure it could be better. The barrel CA guns comes with sucks, and I highly suggest that you replace it immediately, along with the hopup bucking, because that isn't the best out there either and its only $6 to get a pretty good one.
I've owned and handled CA guns before, and overall I'd say they are solid. But if you plan on leaving it how it is, I wouldn't suggest buying it, it needs a new gearbox(including the shell, which may crack in the winter with a powerful enough spring.)
*Need someone to write STAR/Ares and ICS, I have had limited experience with those two.