As of right now, the opinion letter that was sent stated incidentally shouldering the device didn't constitute redesign, but deliberately altering it, (removal of nylon strap on some, changing length of pull to be useless as a brace, etc.) would then constitute a redesign thus making the firearm into a Short Barreled Rifle, thus subject to all NFA rules. I believe that opinion letter was addressed to only one actual manufacturer, but is being held through oral contacts with ATFE as being applicable to all Arm Brace manufacturers. I am not a lawyer, nor do I play one on TV, but my understanding is that if you shoulder your TailHook as an incidental act, it will not be considered an illegal act. This is not legal advice and should not be taken as such, your mileage may vary, subject to availability, not available in all states, no refunds or returns, do not use in the shower, not to be used as a safety device and subject to verification.