Can't put a vertical grip on a pistol. However....
The ATF defines a vertical forgrip as a grip that is 90 degrees from the barrel. This grip is not a 90 degree grip so....? Not recommending this for an AR pistol.. just throwing this thought out there.
According to ATF ruling, if the overall length of your pistol is greater than 26 inches, you can add a vertical foregrip. that's with the brace in the folded position or fully collapsed position and no removable muzzle devices attached to your barrel, for measuring purposes. That's as of July 10, 2019. Haven't seen anything else on it.
To summarize … unless your AR pistol has an OAL greater than 26 inches then you should not add a vertical fore-grip unless you first submit a Form 1 and get it approved.. if u have a folding stock measure it from the folded Position
As by ATF new firearms definition, it would be illegal to use a vertical grip on a AR pistol.
Even though this grip has a slight angle, the ATF ruled this specific grip as a vertical grip. As such, it could only be used on something fitting their measurements for a rifle.
People on Arfcom have been doing it but I feel like it's something the ATF would probably shoot your dog over. There's only been one opinion letter giving it the okay, I'd wait for like 12 of them like with the braces and AFGs.