Those Sprint booster boxes don't look like the best option in my opinion because apart from anything else they effectively make the last 25% of physical throttle travel completely pointless (i.e that last 25% of travel does absolutely nothing whatsoever). As you can see from their own graphs and technical explanation, the output voltage is maximised at 75% throttle. So the only advantage over the stock configuration is the reduction of time-lag between the time it takes for your right foot to press down on the pedal to the desired throttle opening - simply because there is now effectively a handful of cm less total physical travel needed to produce the same output from the throttle position hall sensor. So yes, that will help but in my view it is better to simply train your right foot to be less lazy and thus retain the advantage of a more linear throttle response whilst also knowing that if you press the throttle down those last few cm, the performance will still improve. To me it might almost be a little dangerous driving a car where the throttle pedal simply does nothing for the last x cm of travel. A driver will expect that if they are at 75% throttle then nail it completely, the car will do something. But with this it does nothing whatsoever.
Incidentally, all the high performance cars I have ever driven have had linear throttle mapping. I remember test driving a Focus RS and not being impressed with the performance compared to my old Mazda 2! That was totally the doing of the throttle mapping. Put the foot down and obviously the story was completely different. Same with a Porsche 911 and a Commodore V8 I drove. Linear throttle is much better!
That said, if you compare my 2006 Yaris to my 2014 Corolla, the Yaris has much more aggressive (stock factory) throttle mapping but unlike the Sprint Booster, the mapping covers the entire physical throttle travel. The difference is of course the response is not linear on my Yaris - you might get about 50% throttle response at 30% physical travel (so yes, it does feel "nippy" at light throttle compared to my Corolla) but then you get less performance reward when you put your foot further down. This is unlike the Corolla where the response is linear and more like what you would have gotten with a cable throttle. Put it this way, if there was a performance contest between my Corolla and my Yaris at a maximum of 50% throttle travel, the Yaris would easily win. But if you nailed the throttle, the Corolla would easily win.
So the problem with all these throttle pedal based solutions is that they do not actually solve the real problem which is the time taken for the ECU to process the physical accelerator pedal position data, calculate the required butterfly valve position (or valve positions in the case of the ValveMatic) and then actually effect that mechanical adjustment within the engine. That is the real problem with modern cars.
There are better ways to improve the iM throttle response, one being exhaust modifications and another being intake modifications. Neither are going to make the car feel like it has a mechanical throttle but they definitely improve the response. I couldn't even heel and toe downshift properly in my stock Corolla because the throttle lag was so bad it just took too long for the engine revs to rise before I was ready to engage a lower gear. But after getting the TRD exhaust and changing the air filter to the HKS, I can now shift down properly with no problems.
So far as these electronic boxes are concerned, I'd be more inclined to recommend the more sophisticated ones that map the entire physical travel of the pedal but have non-linear response curves. At least that way you still benefit from the entire travel of the pedal - it is just that most of the performance is on-tap in the middle range of travel with increasingly less as the pedal goes down to the floor (as is the case with my stock Yaris as previously mentioned).
