I did some of the initial testing on the Exotek chassis for the TCX. In comparison to the optional narrow HB chassis, I found it creates a more stable car with more rear grip. The HB chassis makes the car more reactive and aggressive overall. For lower traction or unpredictable conditions (unprepared parking lot tracks, cold conditions, inconsistent carpet), I prefered the Exotek chassis.
For more prepared racing surfaces, I usually chose the optional HB chassis. It's stiffer, and seems to change the balance of the car to have more initial bite, and transition better.
Now with that said, I have not been keeping up to date on Mike's latest offerings from Exotek. All of his products are great though