The upside of the decision is that the administrative entity has been properly limited; the ATF does not have the authority to make such declarations.
The downside is that some day, the Congress may take action; that would be the Constitutional approach.
The misunderstanding of the topic centers around a false belief that bump-stocks enable "machinegun like" rates of fire. That is patently wrong.
The rate of fire (RoF) is governed by the design of the components in combination with the ammunition used. The weight of the bolt, buffer (if present), the recoil spring force, the gas porting (if present), and the pressure of the cartridge all play into the RoF.
Bump-firing is completely possible (and done fairly easily with practice) irrespective if a bump-stock is present or not. (see any YT video on the topic of bump firing) ... Bump-stocks do NOT make a semi-auto into a full-auto. Rather, bump-stocks merely enhance a recoil-driven process where some people lack skill to manipulate the arm without such aid. To be clear, bump-stocks do NOT alter the RoF the arm is capable of. What they do is enhance the ability of the shooter. Those are very distinct and important differences.
So, as an accessory, the bump-stock merely allows the user to more closely approach the full potential of bump-firing; bump stocks do not, in and of themselves, make bump-fire exist in the absence of anything else. Bump-stocks are a tool for those who do not have the skill to bump-fire.
Could they be banned by Congress in the future? Sure. But would that not be a dangerous precedent? After all, don't we have a slew of other accessories that allow the user to enhance the useful nature of the arm?
- Scopes help increase identification of a target at distance. Scopes do not make the rifle shoot further, but they do improve the odds of hitting the target at longer distances.
- Grips help improve the control of the item. Grips allow one to get a more comfortable purchase of the arm, and control it in rapid fire, and reduce flinching, etc.
- Slings can be used as a control aid. Slings, when used properly, are not just for carrying the arm; they can be a tool to steady one's posture, thereby reducing poa (point of aim) variation when trying to acquire a target
- support devices (bi-pods; tri-pods) help steady the point of aim also; these enhance the ability to put the round on target. They don't make the gun more accurate, but they do improve the shooter's ability to maximize the arm's potential.
These are all accessories that improve the shooting condition. They do nothing to alter the maximum potential of the arm. These accessories enhance the skill (or lack thereof) of the shooter.
If bump-stocks as accessories are banned, what's next???