So apparently there will be two versions of this brace for ARs... the SBPDW from SB Tactical that uses a milspec buffer/spring, uses a carbine-length buffer tube, does not have QD mounts and costs $300 or so, and Maxim's brace version of their CQB stock that follows the same pricing structure as their stock version, and includes their proprietary JP silent buffer or proprietary buffer/spring and is 1" shorter than a normal carbine tube.
It seems a bit misleading to me, as SB Tactical has been putting up pictures of the Maxim version around the internet and at shows, etc but in the end it doesn't look like that's what you'll get from them or for the price point.
This is the latest photo on their facebook of the SBPDW, which they explained to me is 1" longer than the Maxim CQB stock due to using a milspec carbine buffer/spring.
And here is Maxim's photo from their Facebook. Pricing MSRP is same as their stock... $395 for the brace kit including a standard proprietary buffer/spring, going up from there... $450 for the brace kit with the JP silent spring.