Fet's are what transmit the power form the battery to the motor. Their real name is MOSFET: Metal Oxide Semiconductor Field Effect Transistor. The more of them there are the more power a device (ESC) can handle. OK enough with the electronics lesson. I run the RS in all of my 10th scale stuff and have been very happy with it. I was going to by RS pros but after speaking with Randy on the Tekin RS thread he said it is overkill for off road and suggested to not spend the extra money (imagine that a honest company rep.) I have ran them for about a year and a half now with no problems. I have run as low as a 8.5 and to be honest it is way to fast! If you have a hooked up track surface you may be OK. With the hot wire it really wakes up the ESC especially for the higher turns. If you are running 4wd you may want to go with the pro to keep it from thermaling but in 2wd yo will be just fine.