My primary concern about this stupid order is that it's just another highlight of a lame duck president that abuses and over-reaches when he can't get his way.
Also, I can see very easily how these orders could be abused, and could inconvenience innocent people like, say, hobbyists who mill blank receivers for a few bucks. What was once a cheap service from a friendly machinist is now a firearms dealer, since the receive is generally viewed as the part of the gun that makes it a gun.
Also, you probably would now need a background check and fees for transferring a legal firearm to a family member.
This would also, likely, mean that people who buy relic weapons and black powder firearms for a hobby (hardly effective weapons), would need to do these background checks.
It's a pointless stupid law that does hardly any good and just increases the tax burden and difficulty of a lawful citizen to obtain a legal firearm.
The only part I agree about is the increased number of background check staff for the FBI. They frequently miss the window for those checks.