Most shooters have found their natural point of aim using the dominant eye and primary hand. Use the full-length mirror to see it using the other hand and to help guide the body into unfamiliar territory.
Shooting with the support hand is probably a skill which most officers will never need over their entire careers. However, the officer who does need this skill will be thankful he familiarized himself with it.
Lindsey Bertomen is a retired police officer who teaches at Hartnell College in Salinas, California.