SB Tactical knew how the game was to be played because they submitted the SB1 and got ATF approval. They failed to do so with all the other braces. As much as I like to say FATF this was a poor business decision on SBT's part and now they got their hand slapped.On the flip side, not submitting them for "approval" also doesnt make them illegal.
It just means they may or may not be "designed to be fired by one hand" and the ATF has not made an opinion.
But there is also no real "approval". If there was actual "approval" the bump stock ban would not have been allowed.
There is only opinion letters that the ATF issues about if they believe something complies with the law at the time the write the letter and how they are currently interpreting the law.