It seems to turn off the start/stop even before you start the car - the light comes on when you open the door - but yeah, it's just simulating the button being pressed. Couple of logic gates is likely all it is. No permanent modifications to the car. As you say, easily removed if you're worried about it.I doubt it, it seems to just have a little computer in it that clicks the button once the car turns on. If you're concerned you can remove it before you take it in for service. As far as I can tell it just clicks the button for you electronically.
I bet it doesn't even store an error code. I think the net effect is the same as if you hold the button down as you start the car, but with the added benefit of another button press turning it back on.the only thing the dealer will see if you uninstall before a service is a code stored for the error.