Interested in one because they last longer, safer, faster charge rates etc. Not sure but I would think it might effect servo speed due to the decreased voltage amount.

Has anyone used this type of battery in a TC car and what are results compared to lipo?

I have messed around with the LiFe chemistry batt. Voltage to the servo is not a problem as servos are designed to run at that voltage. It is my understanding that the ESC/receiver will drop the voltage down to 6 volts max to the servo anyway.

Everything you stated above is true, but for an RC application the battery poses a few issues.

The first is as you pointed out, it is not a voltage that is common with RC racing. If you don't race, then this will not be a problem. If you do, then you will be at a disadvantage running at 6.6v (2S) or a significant advantage running 9.9v (3S) and common rules for TC do not allow this battery.

The second issue is size. The standard size of the cell is not a sub-c. However, I believe that max-amps makes a LiFe package that can be mounted in most cars that can run a lipo pack.

LiFe batteries require a larger volume and mass than a LiPo of equivalent energy.

For a bashing around, I think LiFe is a fantastic technology with the quick recharge, safety advantage, less issues with accidental deep discharge, and high current discharge C capabilities. Just don't expect it to displace LiPo at your local race any time soon.

The few rcvrs I've checked the output voltage on have all been 6.0v - Futaba and some Hitecs, so the servos won't see any diff.