It's arguable that a SBR is the "best bang for your buck." We here it a lot, look at what is required vs an AR Pistol.
A SBR is a "rifle," which means it's not legal to conceal carry in many jurisdictions. The pistol can be - which also goes to how it's transported. A pistol falls under CCW provisions in many state laws, which allow it to be loaded and ready to hand. The rifle falls under anti poaching rules in the law, which requires it to be unloaded cased in the trunk. Your state laws apply.
As said, the SBR requires prior approval by the ATF to be transported across state lines, the pistol doesn't. It does need to be considered if the other state allows them - NJ comes to mind as the extreme problem.
In use, the SBR and pistol can be identical in almost every respect - the ATF has no barrel length requirement for a pistol. It's the stock that becomes the issue, ballistically they are otherwise equal. What has to be answered is whether a stock and it's inherent accuracy is needed. First, the purpose of a short barreled weapon should be obvious, use and carry doesn't allow a longer one. We are trading off range, therefore, for immediacy of having the weapon and being able to use it where longer barrels are a disadvantage.
Because of that, the typical 10.5" barrel is limited to being used at less than 100m, and more likely, less than 50 feet by application. Most are selected for ship boarding operations or in built up urban areas, llne of sight is limited.
At 100 meters the average target is the human torso, about 18" square - or 18 Minute of Angle. How accurate do you need to be to get a hit on that? If your skill level requires you to use a stock, ok, but for a lot of us, not so much.
And at this point, does getting a Stamp and owing an SBR become a rite of passage, sort of like buying into the Man card club?
Again, for a lot of us, not so much.
That is why it needs to be examined what the specific conditions are for the individual owner in his state jurisdiction - and what his skill level is. And it does have to be mentioned that after a trust and/or other legal requirements are met, the owner is registered with the ATF as much as the firearm is. There is a loss of privacy doing that, doesn't bother some, for others, not so much.
To say that an SBR is the "best bang for the buck" isn't a true statement for everyone across the board. It may be, in fact, the least optimum decision to make. If the gun is meant to be useful in self defense it's not going to be helpful to have it locked unloaded in the trunk.