Most of the servo testers are probably close enough to center things up for a build. If I need accuracy, I use an oscilloscope to set them to exactly 1.5mS. Rarely needed though. As for the lack of a detent position, I agree. How hard would it be to put a detent in there at center? Instead, I put a mark at center as compared to the transmitter center and it always works out to less than one tooth on the servo arm.