There are 2 reasons why the S197's have this "throttle lag" with our drive-by-wire set up:
1- The tune. Your tuner should be able to adjust for this to make your throttle more sensitive. He just needs to increase the signal for the different throttle positions. I think there are 10 or so.
2- The actuators in the pedal assembly. Inside the box where your pedal is located there are a series of brushes that run across some metal contacts, and that is how the car knows where the pedal is. Some cars, because of manufacturing tolerences, have some dead space where you actually move the pedal, but not far enough for the brushes to make contact with the little metal contact strips. This is the physical throttle lag that we may encounter.
Solution to reason 1 can be had through your tuner. I run Bama's race tune in my car which has really good scale for the throttle response, but did not remove that dead space where the computer did not know that I actually moved the pedal.
Solution to reason 2 can be resolved a number of ways. I've seen guys open up that box and bend the brushes to where the were contacting the metal strips in the right spot. This did not sound very appealing to me. The brushes have like 10 little wire bristles or wires on each that need to be bent with little jewelers pliers, and I think there are 4 or five brushes, I can't remember.
The second solution is to actually make a little like bump stop for the pedal arm where it enters the actuator box. Basically I put a couple pieces of double sided foam adhesive tape, (with only one side sticky) on the arm where it contact the edge of the box. This makes the pedal not return all the way back up, thus it is like holding the pedal down just a touch, eliminating that fraction of an inch dead space. No it does not effect the idle at all. I am going to put something more permanent and durable in there, like some lead tape I use for weighting my golf clubs. I first did it just to see if it would actually work.
Don't spend that kind of money for that thing. It doesn't say how it removes the throttle lag, but I suspect it works the same as other units that I have seen for imports with DBW throttles. It probably just ups the voltage signal from the throttle to the computer. You can do that through your local or internet tuner. I guess it's kinda like a boost-a-throttle (I just made that up). It probably doesn't address the physical input side of the equation. that you have to do by making physical mods to your throttle.