I've had a few generations of Braun shavers and I've tested this with each one ... and it isn't true, the Braun foil doesn't cut on its own. I also use Panasonic shavers. In my experience, Braun shaves very well dry and Panasonic shaves very well wet. Haven't used a Norelco in about 15 years.
I understand. What they're looking for is a degree of sharpness. Every Rav has a different level, but most base it on how the blade or foil feels to the touch, without trying to shave with it.
What needs to be understood is that for many rabbonim the default status is assur until they're confident otherwise. So it's not something you can necessarily disprove or prove, nor is it particularly scientific.