Don't get worked up about some of the chatter - I personally think there's a lot of "my choice rocks and everything else is garbage" going on.
With M855, your Stag should be good to go, Plus Package or no. I have found the quality of my Stags to be excellent. I chose to go with Stag lowers for 8 of my non-Stag uppers, and have been very happy with them. The only non-Stag separate lower I have is a Spikes.
I have never had an issue with any of my Stags (4 of them, including both lefty and righty models). If trouble happened, I'd be perfectly happy to pick one of them up and trust my life to it.
For context, I have 5 Colts (3 LE6940s and 2 LT6720Rs), 2 LWRCs, 2 Noveskes, 2 LMT MRPs, a Bushmaster patrol carbine, a POF 415, a Sig 556, an FS2000, a PS90, 2 ACRs, a pair of SCARs (one 16 and one 17) and the four Stags. Added to that, I have 2 POF 415 uppers, 2 DD M4 uppers, 2 Sig 516 uppers and a White Oak custom build. Nothing that causes me problems stays in the stable, and the Stags are sticking around.