I would echo what buddfridge says above.
It is quite hard to explain and to me the person that best explains the way the pedal box works is Exonian so maybe he will be able to help explain.
The first 25% or inch of pedal travel is where the effect of the pedal box is most noticeable, no doubt as that is the area where the standard response is so lacking and ineffectual. Of course it affects throttle response the whole way down but as above you simply adjust foot pressure and adapt your foot input to achieve the response you desire. So those with a heavy right foot (myself) will, probably, without really realising, find they have a lighter foot over time as a result. I haven't given it a great deal of thought but thinking about it now, I definitely use less foot pressure and feather the throttle more driving with the pedal box, but it's not felt like a sudden change at all or that I've had to learn a new style, it is simply an intuitive evolutionary adaptation to the the altered throttle response. And don't forget you have full control over the box as it is highly customisable so at the touch of a button on the controller, the response can be subdued to suit (or increased).
I've never modified any of my cars with anything of this kind, usually happy with standard setup, but after several months of driving the R, the standard the pedal response, namely the first 25%, was properly spoiling my driving enjoyment of what is and otherwise fantastic car. Knowing there was an easy solution and having asked the opinions of lots pedal box users via forums, I decided to go for it. All I can say is I wish I hadn't waited so long. The car with the pedal box is now 100% enjoyable, the missing 25%, of both throttle response and enjoyment, instantly fulfilled by the installation of the pedal box.