My 2p for what it's worth. I paid Celtic £150 for a remap file for my Honda CRV. I have the necessary cable and software to apply the map. Got to say I was massively disappointed with it and when I emailed them about it I was brushed aside.
I've had a few cars remapped and this one has to be the worst for feeling a difference
..This gets to the core of the problem..i had my 68 Morris Cooper S rolling roaded for a retune...top top job......to get max out of every engine component.. safely !!.. ......... as far as a C class C250 CGI remap/Ecu power tuning it worries me that to much stress will be put on engine/gearbox to the detriment of engine life expectancy ...Its already quick enough 149...top speed of any standard model is 155 lim ?!!.....I see the fun in extra power but don't see the point .. I would have bought a c350 if that were the case.. ps the petrol versions are very good.. I have never owned any diesel car in nearly 40 years of driving.. foxy52