I used to think chain checkers were a gimmick until I measured 0.75 on a customer's bike
I always told folks to just eyeball the chain stretch by pulling it off the front ring, and it worked fine for my own bikes. Then last Tuesday a guy brought in a Trek with only 1,100 miles on it and my Park CC-3.2 dropped right in, meaning his cassette and chainrings were already toast. Now I'm wondering how many drivetrains I cost people by not just buying the $12 tool sooner.