Considering there are US companies offering single supercharger kits for over $10k less that provide more power it's no wonder G-Power kits are not very popular. Not to mention if you want more power from G-Power their higher boost SKII kit starts at $32,500. Seriously. Even though it uses the same ASA superchargers as the SKI and just runs slightly modified software plus 2 psi more boost. BMW tax anyone?
The new single supercharger G-Power SK Plus offering starts at $9997.35. Only 4.4 psi of boost is run and the system is not intercooled. That is likely why power output is claimed at only being bumped up to 580 horses from 500 which, well, is weak for $10k.
They do have an intercooled option available with boost at 7.2 psi for $13,010.25. Now this is definitely comparable to what you can get from other companies although the Vortech superchargers G-Powers competitors are using likely have more power capability. The ASA blower (depending on which model, as G-Power does not specify which ASA blower they are using) likely will offer greater response down low but it will not have the same top end flow capability of the Vortech units.
That said, G-Power will raise the boost to 8.6 psi with this system in an SKII offering which includes high flow cats for $19,857.75. At that price point this makes absolutely no sense as one could buy the SKI system, get some test pipes, and change the pulley themselves having more power with a spare $7k in their pocket.
In all honesty, there are better options than G-Power on the market especially for those in the USA. The G-Power stuff is well tuned and the hardware is fairly good quality but this is too little, too late, for too much. Additionally, where are the dynos and the blower specs? What about some performance numbers? What G-Power truly excels at is marketing to those who don't know any better. That is why they can get away with calling themselves the leader in BMW aftermarket supercharger systems when they clearly are not.