We done a prototype set on an S15 a while back.
While it "does" work, generally speaking it isn't really worth it.
It a lot of work to put it in, even with the simple system that we had.
It is another moving part, and it is only useful to raise the car up to get over speed bumps.
You cannot drive at the raise position as your suspension will be fully extended.
If you have a ultra low car and you just want to get over speed bump, it isn't a bad option.
We are looking into putting a kit together for this.
We have this working on a BMW and found a few minor bugs, so we have to make some custom parts to get things working 100%.
The only issue is room.
If you want the Air Cup to do anything, it will take up a large amount of room.
With that said, it means the suspension need to have the room available for the cup and the springs.
With the BMW, it was difficult as there just isn't the room.
With the GTR, it would be a bit better as it is quite long.
Also, as I have said, it is only useful for getting over speed bumps.
So most owners will only get the front because raising the rear is an extra cost and counter productive...