Even though it's probably going to be quite a while before I can start, I'm already planning my next AR build. It's going to be an SBR of some kind, either a 9"-10.5" .300 Blackout or an 11.5"-12.5" 5.56, that's optimized for use with a suppressor.

One possibility I'm considering, especially if I choose to go with a shorter-barreled .300 BLK, is a PDW-style stock assembly. I think the concept is interesting and they look really cool, but I don't know much about them. I know they pretty much all require at the very least a custom buffer, buffer spring, and receiver extension, and some require custom BCG's as well, but that's about it. Would they negatively effect reliability? Are they actually useful (for storage and transportation), or are they just a gimmick? Does anyone have first-hand experience with an AR PDW stock? Is there anything else I should know?

As always, thanks in advance.

There is a new recoil system coming out that uses a standard BCG but it's receiver extension (buffer tube) is only 3 5/8 of an inch long (aprox).    Fingers crossed as to when it hits the market, but with a 3 5/8 buffer tube I think most PDW type stocks could be mounted without using a funky proprietary bolt carrier.   

I'm sort-of-kind-of leaning towards the Maxim Defense PDW stock because it looks like you can get a decent cheekweld with it, and it's also available as an arm brace or "cheek rest," so I can build up the gun as a pistol, then swap the brace or rest out for the actual stock with minimum effort once the tax stamp comes back.