"Bump stocks" were approved for sale by the Obama administration.
I have no use for such things, (I was a sharpshooter, which means we conserved ammo and made single shots count), but I should mention that, on an AR platform, their action can be duplicated with a leather belt.
Banning them will make politicians, media, and non-veterans feel better, but it doesn't really change much.
Please don't make belts illegal. I'd have to walk around all day holding my pants up.