One nice thing about the turners is that it provides a definite start/stop. You can't go over PAR... the target disappears. It pushes you.

I know I talk about consistency all the time, but I think using the turner really helps develop that priority compared to a shot timer. The shot timer has an allure to see a lower number each time and to obsess over the number, whereas the turning target gives you a pass/fail report and nothing else. And by taking tenths off your exposure, you push yourself at a consistent pace instead of just racing racing racing.