ok, just a thought.
you say that there isnt any evidence to prove that they work so to you that means they dont. i cant think of any single thing that is proved to make you faster can you, does that mean nothing is gonna help you?

at the opposite end of it can you think of anything that proves they dont work?

impossible to put improvment or lack of it down to one thing. Training with PCs is just as likley to make you 2 or 20mph quicker than training with anything else