A had a huge argument about this with someone a long time ago... you can call Atomicmods if you don't believe my side of the arguement to verify. As it works like a FET upgrade alowing you to run at higher voltages to the motor, it ALSO regulates and cleans the volts going to the servo.
Here is a Link, I don't know if they make them anymore but they are like $45.00 or somthing.
http://www.xmodsource.com/forum/showthread.php?t=15461