Yah, it's OK until the ATFE changes their minds and says it's not. Just ask anyone who paid close to $1000 for the Akins' stock. It was a bump fire stock for the 10-22 and got the ATFE's OK in the beginning also, until they changed their mind and ruled it a MG, which made it illegal to own for anyone who was not a SOT, gov't, or LEO.
THISNot everyone cares about accuracy or printing groups on paper. Shooting is supposed to be fun. Sometimes throwing a lot of lead down range is fun, and they have every right to do so. Too many antis against gun owners for us to fight amongst ourselves.