Haven't tried it with a straight yet, but 95% of my shaving is in the shower with no mirror whatsoever. When trying to shave the back of you head and sides a mirror is useless, unless you want to use 2 or 3 of them.

Ok, so the first year I cut myself once a week ... now I am down to maybe once a month. You do get to know every hair on your head by shaving "blind".