These mechanisms don't really release at a specific tension and it's definitely not supposed to be a surprise. They release abruptly as you rotate the handle and with practice, this can make the archer much more consistent as you go from fully drawn to released in a fraction of the time you could releasing the drawn bow with your soft fingers.

When you release a bow with your fingers there is a much higher chance that you impart some force on the string (and bow) which means your arrows aren't going to fly true.