I'm familiar with the engineers (and sales) description of "air balancing". Similar goals are accomplished with a single mechanical spring with the exception of "let off" after pressure is removed. In both designs, air pressure is opposed by an arrangement of springs; it is as simple as that. Except for price, it is not particularly important that one design uses two springs and the other, a single spring. All regulators are balanced in the sense that all parts are in stasis (static balance) until air flows. After that, the parts are in temporary dynamic balance. However, aside from the engineering, there is the diver's lexicon. US Divers originally used the term "balance" to describe a proprietary design in their revolutionary first stage. To have this coopted and twisted in the name of engineering is somewhat insulting and unsettling. It is a misrepresentation (or ignorance) on the part of Scubapro to gain commercial advantage. This kind of manipulation of language interferes with the ability of new divers and some not so new as to understand the function and value of competing regulator designs. As far as "balance" applied to various first stage designs, whether these designs involve floating orifice's or "flow through" pistons, I have no problem with that. These alternative designs actually do function as balance valves as understood by divers (including engineers), eg, to stabilize interstage pressures.
For those who care about these things, the Scubapro second stage is spring operated with a dual system, mechanical and pneumatic. The pneumatic helper spring is a classic piston and barrel. The amount of spring force exerted by the pneumatic spring is determined by air pressure and size of the piston. In other words, the design translates air pressure to a specific spring force through selection of the size of the piston and barrel. Theoretically, any amount of force could be applied by reducing or enlarging the piston. Thus, the force is applied by a mechanical device, not air pressure per se which means that "air balancing" was not even a consideration beyond that which applies to any regulator design, eg, to install just the right amount of balance between air pressure and opposing spring force. The real goal was poppet "let off" without disrupting the primary function, breathing. Scubapro engineers were looking for a compromise which would not throw the regulator into a tizzy but still have some effect. Thus, the force applied by the piston is a compromise between flow and stability. If the piston were too large, the whole thing would go into free flow as soon as the poppet was upset. If too small, the pneumatic spring would not be functional and all the load would be carried by the mechanical spring alone. So, one can see that the design is not a simple matter of air pressure pushing against one side of the poppet and equal, opposing pressure on the other side. The "balance chamber" is actually a piston ram which applies a predetermined force to assist the primary spring.
This design was a huge commercial success mostly due to the mystique of "balancing". However, efforts to unload the poppet continued with various results but all added some complication. If my opinion were sought on this matter, I would give the nod to Sherwood's SR-1 floating orifice which is simple and effective.
One can't just go around calling things whatever they like. Of course, they do and they get away with it. The usual motive is political advantage or commercial gain. In this small instance, the question of what to call a regulator part, a company glamorized a mundane pneumatic spring by asserting that it was something else and had special properties which were all out of proportion to fact. It is an easy game to play if one has an advertising budget and duplicitous or ignorant people posing as instructors representing some organization with an impressive name. So, if Scubapro were to order them to say that a balloon was actually a "balanced sphere" and a teeter totter was to be referred to as a "balanced beam" they would try hard to sell the toys with a fancy name and price to match. What is scary is that they might succeed.
