Why use a super accurate cartridge protractor

In discussions about cartridge setup, there are those who say that unless one has a cartridge setup protractor like the Mint, Wally Tractor, Dennesen, etc. one cannot expect to extract maximum performance from your rig. Then there are those that say that even the best alignment tool still only nets you a position that needs further tweaking by ear. In my case, I've used a Dennesen and a number of downloadable free protractors and have been able to get good results with the free downloads if I took my time to make those little .5mm shifts that make sound pop into best focus. Is the superiority of a Mint or a Wally Tractor because one doesn't have to make those final last tiny adjustments? Is it that the mirror surface is easier on the eyes?