simply ask them if they have a valid state department issued export liscence for firearm parts and accessories...... if they don't , and they ship to you, US laws are being broken...
if the part is a flash hider and it is advertised as for the m14 , then it IS a controlled part in the US and is NOT legally exportable period. Muzzle brakes are not under the controlled list and are exportable..... the US views flash hiders in general as a "military" rifle part and not for civillian export.