I agree with Brandon on the LSD, but only if you are going to be using the car for a lot track time or autocrossing. For the daily driver that rarely gets on track, I would not spend the money. Locking the armrest down to keep Pennywise out would be a good mod. From what I understand, the Fiesta ST doesn't employ an electronic diff, in the sense of a mechanical diff being controlled via electronics. Wanted to add that for clarification concerning an eDiff.