SP regulator packages have everything to do with marketing in that they create entry level, intermediate and advanced level regulators, but are not always the most economical way to get good or even great performance.
Personally, the balanced nature of a balanced second stage will even out most of the IP change that occurs with an unbalanced first stage. The result will be better breathing performance through the entire dive than you would normally get with an unbalanced second stage.
Plus most balanced second stages are capable of higher flow rates than unbalanced second stages, so they will deliver more performance out of even a Mk 2 Plus with it's "only" 90 SCFM flow rate than would a lower performance unbalanced first stage.
The opposite approach of putting a balanced first stage with an unbalanced second stage also has benefits. The balanced first stage allows the unbalanced second stage to operate a constant intermediate pressure and allows it to be tuned for a lighter inhalation effort. It remains the weak link in the system as far as shear flow rate, and will not give the same raw performance as a balanced first and second combination, but within those limits it will allow a lower inhalation effort from the unbalanced second stage.
Personally, I use unbalanced Mk 3's, Mk 200's, etc with balanced second stages on my deco bottles. This apporach gives me compact, light weight, very simple and reliable first stage that still warns me of a near empty deco bottle with higher inhalation efforts at very low tank pressures (around 200-300 psi) but also allows me to get very low inhaltion rates and comfortable breathing during long deco stops. It's the best of both worlds.
