Handstops have been in existence in the shooting world for years. They have been used as the name implies - for short weapons, placed in a way to prevent the hand moving forward of the muzzle, or as barricade points to hold against cover while shooting.
I put one on my Mk18/Commando, intending to use it as a hand stop. Now I have been fencing Epee for a while now and I immediately saw some parallels in the feel of these "hand stops" with the pistol grip on my Leon Paul Epee.
The epee pistol grip (otherwise known as the anatomical or orthopedic grip) was originally developed for a 19th century Italian fencing master, L.Visconti. Visconti had lost some fingers in some sort of mishap, and had the grip designed to enhance the leverage of those he had left. This grip has become popular among sports fencers in the late twentieth century because of the way it enhances a fencer's lateral strength for the parry (block), complements the agility and athleticism of competitors.
In high-level fencing, pistol grips are used by a large percentage of epee fencers because they allow stronger and more precise blade movements.
The existing thought on using the VFGs and such is to cam the hand onto the forearm (Magpul AFG), or to use it for pressure (VFG). This concept involes the fingers and the hand. As you recall, the Weaver was into arm pressure, and eventually as Americans became stronger and bigger, everyone realized the best control began in the hands...making the arm position almost irrelevant. These act as index points and pressure points and are more analogous to a competitor's thumbs forward grip than to a VFG/AFG deal. Think finger pressure.
On the rifle, strategically placed for each shooter on the handguard, they allow a similar "feel" to the Epee pistol grip. By using the thumb and index finger on these pressure points (a better and more descriptive term given how I use them), one can keep the muzzle on target, or move it from target to target a little faster and with a little more certainty. Your mileage may vary of course, but I have found them to be a great addition to any carbine or rifle intended for use in fast CQB situations.
Getting the muzzle on target has to do with the hand position. For example...it is easier to get the muzzle pointed with the fingers of the support hand pointing forward than it is by grasping a VFG in a beer can grip. That was part of the concept behind the Magpul AFG. In this case, we discovered that by finger pressure, one can drive the muzzle onto the target with a greater feel for where it is going and with a greater degree of control.
The point is this. The same system that helps an Epee fencer get the point on target accurately allows the shooter to get the muzzle on target accurately. And it is in fact about getting the muzzle on target, not "getting the stock aligned".
Think of the support hand like the spearman's front hand. The rear hand is the power hand, and the front hand is the leading accuracy hand. Same in this case. The front hand drives and steers the weapon's muzzle forward onto the target (the single most important thing to do), and the rear hand works the trigger.