Well; IMO it depends on how often you run your engines.

Ive been using CoolPower for a very long time now, and I yet to see a negative effect on any of my engines - 2 or 4 stroke. I never use ATF as well but I run all my engines almost every weekend for several times.
When ever I open up the back cover for conrod bushing & crank bearing inspection, Its always as shiny as a mirror, with no signs of wear & tear.

I use ATF only when I put an engine to sleep for more than 3 months. Then I fill the crank case with ATF and seal the whole engine off completely with a stretch film.