I've been contemplating picking SRC's CQB M4 RIS and your review helped me make my decision. I'm glad to know it went well for you despite a couple of cosmetic flaws.
I have an SRC M4 CQB it works fine but if you want to upgrade it you should change the motor with and EG1000 because it can't drive the m120 spring and be careful with the hand guard its a little woobly but overall its a nice baby