I have only had the tune for about 10 days or so but here goes.
Mileage: If you drive conservatively, you will get some great numbers...about 24-25 city/mixes and around 30-32 highway 1800-2000rpm
Mileage: If you take advantage of the "HOT", your mileage will return to about stock but with more power...so it is to be expected. In all fairness, it is still maybe better than stock by about 5%
Driveability: It is much more responsive...better feel from the "Go Pedal". It is not a quantum leap in acceleration but it definitely is faster and smoother. It pulls stong over a greater range of rpm and turbo lag is almost non-exisitent. When using "cruise control", not only is the highway mileage better but it shows less "want" to downshift.
Other Things:
1) The temp guage seems to be reading "slightly" cooler than previous and I already had the SEGR.
2) Tip Out of the "Go Pedal" at lower speeds while the tranny is still in the lower gear range takes a bit of getting used to...it seems to keep power on for a split second...especially noticeable in parking lot manuvers.
3) Probably related to #2...it seems that the CRD Coasts a bit easier...no clunking of the drivetrain when you lift like before.
4) Engine noise at idle is more pronounced than stock...but about the same as a SEGR.
5) The turbo whine seems to be more than stock but less than SEGR alone...not sure but seems that way.
Overall: Much better CRD than stock...Better MPGs than stock if you can resist the urge to "floor it"...Even better driveablity than just the SEGR or Unplugged MAF Sensor.
It seems like GDE has tried to duplicate the characteristics of the newer Piezo Injectors with the tuning of the Pilot Injectors with the Fuel Injectors. Better fuel management has definitely inproved the CRD.
If you can not keep your foot "out of it", go for the straight "ECO" and forget the "HOT"...
club. You will get over the skinny pedal syndrome, at least I did? But that might depend on your age