The Cyma nylon receiver is reasonably well made, I assume the metal one is similar. It lacks trades (if you care about that), but the selector switch captions are cut into the receiver. The faux bolt cover is relatively soft plastic, and I had to make a metal backplate for it when I damaged it during assembly of the blaster (the faux bolt activates the mag prime on the Cyma gearbox).
The safety is really nice on my Cyma, positive and not bindey like my ACR. The nylon lower has almost a textured finish, and it takes paint (and dirt!) well. I had to cut down the buffer tube adapter to use a Kublai buffer tube: the Cyma buffer tube is very heavy and slightly smaller in diameter than the Kublai branded one, and I didn’t like the way the stocks wobbled on the Cyma one. The buffer tube adapter on the WAT receiver pictured there looks in between the length of the Cyma nylon and the M4A1 metal wells receiver.
The M4A1 metal wells receiver is fine, though the safety on mine didn’t lock positively into the semi notch and the actual casting is a bit ordinary (mine has a few blemishes in the metal). It doesn’t seem compatible with the type of faux bolt that the Cyma uses because of how the charging handle spring is attached. No trades again. The buffer tube adapter is shorter than the Cyma or the WAT (from the photos), but it worked with the Kublai buffer tube just fine. The “safe semi auto” captions are painted on rather than cut into the metal of the receiver, and are some weird font that doesn’t look quite right. It just feels a bit less refined than some of the other receivers available now, though if you just have to have a metal receiver it is a good price.
The upper from the M4A1 wells receiver doesn’t fit on the Cyma lower. Haven’t tried the other way around.