Performance impact of OnMouse_ event handlers on mobile

There's a warning when targeting Android or iOS and using mouse code. I am trying to keep my interface simple enough that it doesn't need multi-finger touch, so I thought I could get away with making a completely cross-platform control script that relies mouse emulation instead of Input.touches. Is that a bad idea?

I'm not looking forward to rewriting all my input code if I don't have to, especially if it's just to test if there's a real performance difference and to find out that there is not.

But if Unity feels the need to warn me about the performance impact of doing this, but doesn't have anything to say about using .Contains or .IndexOf in a for loop in Update(), it's got to be serious, right?