I'm unusually right handed - mono-dextrous as you might say. Trying to do anything delicate with my left hand is a guaranteed disaster. So although I know everybody recommends learning to shave with both hands I just daren't. Consequently I've gradually worked out ways of reaching all the awkward parts with just the one hand - it can be done, it's just ungainly. But I think the general advice is right and it would be simpler using both hands.