Its a mod for the "Playstation" generation who are used to a digital response have grown up with traction and stability control and don't know about when the only traction control available was dependent on your right foot and stability was all about the feel through the seat of your pants... 
The "pedal box" delivers more throttle opening for a given pedal travel by intercepting the drive-by-wire signal and altering it to increase the "throttle" opening...
Some of the best "drivers cars" I've had/driven have fairly long travel throttle pedals to allow more effective modulation of power to the wheels. This did not detract from the performance or the fun... In fact it probably enhanced it...
But if you like the effect that these pedal boxes give... each to their own...
I usually describe them as actually lowering where the peak HP is produced, they don't increase the peak HP figure at all, but it does increase the HP produced within the lower part of the power curve.
How does it do this? Please explain, I am interested to understand how it does this if it only connects to the pedal? It must be intercepting the signal between the throttle pedal and the ECU as I understand it... what is it doing with this signal to change where peak power is produced?
First off, I'm far from the Playstation generation! My kids are of the generation not me, I'm middle aged and have been around Golf GTIs and other hot hatches since the 80s. That's my generation.
I like my GTIs to drive like GTI's should - not breaking any land speed records but just having a bit of fun within the confines of the law and traffic conditions and actually enjoying my driving instead of treating my car like white goods transport.
I drive quite a lot of cars and vans day to day so I know what a mk7 Golf feels like compared to other cars and so I feel justified in any criticism I level at it and to be honest the power delivery is the only criticism I have of the car that isn't nit picking.
There's no way you can pass judgement on a PedalBox or even a remap or tuning box for that matter unless you've tried one. End of.
It's a bit like the guys on the mk5 forum passing judgement on the mk7 when all they've done is look a a few pictures on the internet and seen Tiff Needell expecting the GTI to be something it's not designed to be in a fairly irrelevant TV article. Possibly VW are partly to blame for that TV article by mentioning the 'Ring in their advertising of the PP GTI but hey ho…
Try it and see for yourself is all I can say.
The PedalBox does nothing to the cars power it just intercepts the accelerator pedal signal and amplifies it just like a tuning box intercepts the ECUs signal. It makes the available power much more accessible rather than increasing it and as Andrew says - it makes it feel like the power comes in earlier as it just makes the car soooooo much easier to drive.
One benefit I've found is that you can trickle along in traffic much easier by just brushing the pedal so rather than making the car feel quicker in those congested situations it just takes the strain out of being in a traffic jam!!
As said, once tried you'd not want to be without it IF you're the right sort of person for one. I've had a version of it for over four years so that says enough I think!!! Even before I'd taken delivery I knew it was the first mod I'd have to do.
It's the same as anything, if you sit on the internet over analysing it then you'll get nowhere; try it...