their power gain is certainly up there with the big marketing companies you say. I've used revo before on my S3 2.0TFSi and didn't like it and switched to FR&RTuning. Also if you look at some of the revo 2.5TFSI reviews lots are going into limp mode because of high EGTs. As for the torque the companies you mention show TTRS with manual boxes this is DSG which limits the torque. You mentioned superchips one of my mates has a astra VXR that was using the Bluefin stage3 software and when dynod at fr&rtuning it was rubbish straight away he asked for them to do a new map which they did more power more torque straight away. And for the price some others charge I not convinced its worth it. Others ive no experience with but are too far from me anyway if there was problems id have to drive and maybe leave the car with them for a few days
FR&R aren't producing the same gains though because they are working from a 360bhp baseline and not 340-350 which most 2.5TFSI's make at MRC, APR, REVO, MTM, DMS etc so they are 10+bhp down and some 50-90NM down as well. s-tronic IIRC is good for some 650NM standard saftey margin and those mapping the s-tronic boxes can take this to 700+NM IIRC for those working the Loba 500 hybrid turbo development.
Personally I'm not keen on REVO because of the EGT issues, the maps are quite old hat, MRC, APR and MTM are at the forefront. As for warranty, MTM, Sportec, Superchips are the only three I know to give warranties that says if the engine muches as a consequence of their map they'll cover it but how easy that will be who knows.
I would rather pay for a company with demonstrable history of mapping the engine / car I want mapped and have references to boot. Also looking for a firm that will map both box and engine.