I've had some dealings with RGuns, not AR related. I won't do business with them again.
From what I've seen, if you buy an upper from them and have a problem with it, their response will very likely be "Too bad".
At your own risk is all that I can say.
i purchased a ar flat top upper from rguns. i am happy with the upper itself but those guys aren't customer service orientated. called in an order for a different upper than i have now, 2 weeks later i was still waiting. gave them another call and they told me it was on back order even though they said it was initially in stock. i canceled that order and a week later i called again to order the 16" flat top full bull barrel and pressed them about availability. that should not be necessary. the upper i got is great just don't let them b.s. you.