What he does that you a DIY'er can not do is put it on a calibrated test bench, and make accurate changes to both the timing curve, and the total advance, as well as the fueling vs rpm, and fueling vs boost. Not to mention all the other little bits of knowledge that he has picked up about what combination of parts works best that comes from building thousands of pumps. No pump building is not rocket science, but it is damn near rocket surgery.
Yup there are lots of people who can build pumps out there, but Gilles to this point is the only one I have come across that has taken a special interest in these pumps in specific, and made them custom to our needs. As far as the big power IDI's in North America, they are all powered by a Gilles pump, think that is a coincidence? Don't think that lots of us tried our own homemade performance pumps first before dropping a grand on pump? Only to go WOW, once we stepped up.
I'm sure you could take a Gilles pump to any half decent pump builder and they could replicate that specific pump, but could they do it for any cheaper??? And what about if you want something other then that pump. All of Gilles pumps are custom, that I know of, you tell him what you are planning on doing and he recommends what he thinks will work the best for that application, if you still have your heart set on another direction he will build the pump as best as he can to you specs I.e: 9mm heads or 14mm heads, cummins cam plates, tdi cam plates, or 1.9 cam plates, Twin turbo, single turbo, nitrous, race car, street car, no smoke, lots of smoke Ect...