You will need to check current ATF guidance before installing anything on your AR pistol because they are subject to change and you want to be certain, but Tyrant Designs advertises this as a "vertical grip," which ATF guidance states you CANNOT use on AR pistols under a certain length.
Julia (or others that know). How does that compare to the ATF letter to Micek (Nov 20, 2013) which gave guidance defining a vertical grip one that '...is distinguished by being both forward of the magazine well and oriented at a perpendicular (90-degree) angle to the bore of the weapon." I don't have a protractor handy but I'd put that angle at 65-70deg. Are you aware of guidance provided since that would negate/supersede the above? Not trying to offer legal advice or be contrary, I legitimately would love to know if my understanding of the rule is flawed.