The ATF reverses their position more than a soccer mom trying to squeeze a SUV into a parking space at Wal-Mart. This happened with the "Hellfire" trigger group, and a lot of other things. What happens is at first they don't see it as a problem, (translated...popular), so they allow it with, "A Letter Of Approval". Then as soon as it is they, "take a second look". This is more apt to happen with devices looking for a way around an existing ATF law already on the books. The Sig Brace looking and acting like a SBR stock, and the Hellfire making a gun full auto that isn't.
If they then ban whatever it is, it gets real expensive for the company to fight them. Remember, the ATF has the taxpayer paying their legal expenses. They will appeal and appeal until the Plaintiff runs out of money. Just like the cigarette manufacturers did in the 70's, when they were sued for causing cancer. I'm not trying to insinuate any of this is right. It's just the way it is with our current legal system.