Well the Nixim piece of rubber has arrived and easily installed. I have so far only tried it with iracing where anyone with a G25 knows the issues with breaking.
At first not sure what to think of it really, somehow I have managed to take .25 secs of my infineon IRL time in the skippy but the break pedal feels well terrible at first anyway. I have taken the castors of my chair and have booked myself in for 100 sessions at the gym with a specialist 'one legged trainer' so I can build up my breaking leg to a suitable level of strength. I'm thinking Roberto Carlos would have trouble pushing the break pedal to the floor now.
Anyway with a bit of playing around with the break pedal calibration and the hire of a hydraulic ram, HPU and the necessary fittings to assist with breaking I seem to have it sorted (only kidding about the hydraulic ram).
Conclusion.
This takes some getting used to, the pressure needed to push the pedal to the floor is probably too much unless you have very well secured pedals and seat to (meh I need a sim cockpit)
It is easier, after much practise and fiddling with calibration, to know when you are reaching threshold breaking. Trail breaking I am finding more difficult at the moment.
FACT...my breaking distances are shorter in iracing.
You could easily make this mod yourself, a piece of high density rubber cut to fit inside the brake pedal spring. I'm sure you could cut a piece from a 'bouncy ball' for instance, I would say it is approximately 15x12x50mm, but unfortunately that is a guess as I forgot to measure mine before I fitted it sorry

.
The Nixim website has good fitting guide with pictures.
For the price of a packet of ciggies including postage it's not too bad, but I suppose that is relative, I would rather be racing than buggering around in toy shops looking for a piece of rubber then ending up in hospital because i've sliced my fingers off with a stanley knife while attempting to mould said rubber.