I've tried the app on two cameras, so far. The first I did not expect to work, because the Mercury II has a rotary shutter, and the spacing between the blades determines the timing. Rotational speed is always the same.

The second is a Ricoh XR-S. I'm not sure how best to read the results. I've attached a screen capture to demonstrate. I am not sure where to read the pulse. The test was at 1/500 sec., so I have placed the cursors at what should be that width.