I know how a lot of people feel about Blackthorn, and I agree that they have NO customer service. However, I will say the kit I got from them came in like 3 days and went together well.
The only problem I had with them was they sent me a rifle recoil spring rather than a carbine recoil spring and it would not lock back. I never tried to shoot it with the incorrect spring as I caught it when I was checking everything out. They sent correct buffer....
I emailed them and told them they sent me the wrong spring, and that I had some other things in my shopping cart with them and just drop the spring in with this order. I never heard back from them after repeated phone calls and emails. I still have a open basket on the webpage with 160 bucks worth of stuff in it. So it cost me a extra 4.95 for the correct spring.
The build went together well with the spring being the only problem. I built it in Dark Earth with most of the brown parts being from MagPul. The hand guards are a no-name M4 carbine, as Magpul does not make a set I could find. It has a DPMS lower and the upper has no marks on it as far as mfg. Same with barrel. I probably will not deal with them again because of their customer support, but the kit is not bad for 389.00.
ETA The MagPul stuff did not come in the kit. I got those else where.