yes and no. True, piggyback does fool ECU. But not in way that pots does. Piggyback fools by creating a map much like a fuzzy-logic map , while pots fools the ECU at all engine rev range and this could be dangerous as it could lead to lean conditions or even knocking. True , u MAYBE can use Arduino, and i being an serious Arduino enthusiast have thought of that option. However i think Arduino don't have enough juice for engine control, afterall what do you expect with a 8-bit 16 Mhz microcontroller. EMS700 itself is 16-bit.
For the dyno part, i dont think they gonna run cheap. Think of it like this, if u want to DIY properly tune your engine, then u got to have some proper tools for it. Dyno tuner usually have wideband Lambda sensor which is expensive so that u can tune your engine AFR, and this we normal people don't have. And then there's the dyno which makes tuning much more easier then doing things on the road. Tuner maybe can lend their "tools" at an hourly rates to DIYist and this can make good business to them. And if that DIYist happens to be a lazy person like me, i would let them tune my engine while i observe. Its a win-win, i install the intercepting system , they tune it, i pay them.
Dont take this seriously mate, afterall this is just my 2-cent opinion. :)