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It is definitely angled enough, and does not advertise itself as a "vertical grip", so it appears ATF legal. Check your specific state laws, but West Virginia does not prohibit one on a pistol. States like NY say that any forward grip on a pistol is illegal, though, so be careful if transporting across state lines.
Yes. they are compatible with Glock magazines
I don’t have any Scorpion mags to test, but I believe this is advertised to hold “double-stack 9mm magazines,” and it is adjustable and surprisingly sturdy right out of the box. If I had to go out on a limb, I’d say yes, as long as your Scorpion mags are made to hold double-stacked 9mm ammo.
Yes, as long as the magazine is the same length as a standard capacity mag.
Yes, If it has a Rail
According to the ATF, a foregrip angled 90 degrees from the bore would classify a pistol as an AOW and be illegal without registration while any foregrip angled greater than 90 degrees would be okay.
Looks to be 5. I had to attach it to a Picatinny rail segment because my handguard is all mlok, and I would recommend cranking down on the hex screw if you go that route because it seemed loose when it felt like I had tightened it quite a bit. I went ahead and cranked it down a bit more, and now it’s solid, and opening up a can of man on it hasn’t affected the grip or its ability to retain full magazines. Do note that it is angled, so other attachments that may be in close proximity to the foregrip may need to be spaced a little further away to make room for your hand and the path of incoming/outgoing magazines.
Yes, S&W double-stacked magazines work! I had to try it myself, and I initially thought they wouldn’t because of how much tightening the retention screw was taking between my polymer Glock mags and my metal M&P mags. I was surprised to find out that I could tighten it enough to hold the S&W mags, however, I will advise caution as the metal magazines are lacking the friction of the polymer ones, and tend to slip out or take a little extra tightening to really be held securely.