Well technically DRS is the only one that's limited to specific parts of the track and it's "unlimited" already in those areas; KERS can be use on anywhere on the track which would make it more useful.
Anyways after trying this out, I don't think KERS is really needed; that super acceleration is nice.
However I should warn people if you use super acceleration, your engine might blow up.
also here. Game crashes after activating the trainer.