I've had my Track Cal installed for a few weeks and that included a long road trip from Windsor to Wasaga Beach to Montreal and back to Windsor (1200+ miles). City mileage is about the same, highway mileage maybe even a tick better. Either way, not a material difference.
There is an impressive difference in pickup on the highway in 6th gear. Worth the $ just for that.
The one downside, after braving multiple epic traffic jams, is that the car is now a bear in bumper to bumper traffic. It bucks like a mule no matter how smoothly I try to get on and off the throttle. Previously, the car actually did pretty well creeping. Luckily I do not encounter much traffic on a day to day basis.