The mandatory helmet rule came in a couple of years ago, and applies to all skaters who have not passed their Stage 5 badge - including adults, and in competitions - and baby synchro skaters. The helments have to be CSA approved HOCKEY helmets - not bike, skiing, etc helmets which do not offer adequate protection for falls on the ice.
My guys have been coaching in Canskate for quite a few years. They have had no problems with the helmet rule: The helmets are light to wear, they generally have "openings" for hearing purposes, and there is no visibility problem for "seeing".
Many clubs had rules requiring helmets up to certain levels; this has standardized it for all clubs and for all coaches.