First, I get that "because you want to" is a good reason to own anything you want that is legal. No hate here. My brother once wanted a 50mm pistol (yes, 50mm not .50 cal). Not really usable, but he wanted it.
Now. the main reason I don't like this is because this is a work around. You say that anti-gunners know nothing about guns and don't know the difference? I don't think that's true of all anti second ammendmenters. When we seek a "work around" for an existing rule, we look like we're underhanded. This was the case with bump stocks, and that issue created a lot of hate and discontent. Personally, I don't think there should be a law against rifles or shotguns under a certain length, since we all know criminals don't follow rules anyway, but those rules do exist. For that matter, I should be able to own a fully auto SMG without jumping through hoops, but there you are.
To answer how "useful" these are in the woods or in the car, or inside a house; so is a standard pistol shooting a pistol caliber round. If you are shooting far enough to take advantage of a rifle cartridge, you are better off with a rifle length barrel for which that cartridge was designed. If you are in the truck, deep woods, house, where ranges are limited, even a 7.5" barrel is more bulky than a standard sized pistol, and you generally get the added benefit of a larger projectile, though less velocity (read less recoil). Hence, I consider these arguments egocentric, though as I have said before, that's okay with ME.
Again, I have no problem with anyone owning anything legally, but I think we need to be careful not to be cavalier about the situation.