I don't need a mirror to shave — I know where my face is by now.
I do use an electric hair-clipper to shave the longer head hairs before using a safety razor. Some Vinaya experts will say that amounts to using scissors, but that misses the point. Its just a tool to make the job of shaving quicker and easier.
The scissors rule is about not grooming long hair to fashion it like barbers do for lay people.
In Burma, they still use open razors, and some monks shave their own heads with them too, but I prefer a standard safety razor.