I just bought the King Arms Colt M4a1 and so far my initial impressions is that it seems very solid and everyone at the store said that even though the gear box is harder to upgrade, it is rock solid reliable so you won't need to modify it.
It seems alot of other people have the same gun so the knowledge base out there on tips and mods is quite vast. I always like to know there is a lot of support for a product before I buy it.
My only slight gripe is the mag release/catch. It seems that I really have to slam the Mag into the well to engage it and it doesn't seem to fall out as easily as other brands. I thought it was just an isolated incident until I went to the store and tried out the display King Arms M4 and it was exactly like that too. None of the other m4 from other brands had that issue. Anyone know of a simple fix? I have already lubricated the mag release.