Your Cat 2 friend's advice is highly anecdotal. For more anecdotes, regard how many riders in the pro peloton ride with zero-set-back seatposts (zero).

You will undoubtedly experience higher power output, briefly. Cycling is an endurance sport and you will not be able to maintain a steady output for as long as you could with a proper seat position.

Now, this is assuming your old position wasn't TOO far back to begin with, but zero-set-back posts are usually used by triathletes converting road bikes to a tri position.