[sinistral]

Originally Posted by Marshall

It's always been more about aesthetics than function.

I was going to say that it’s more of a fashion thing—there are excellent tuners in each variety.

As part of its reimagining (and proto-reimagining of Styles 18 and 21), Martin switched back to open-back tuners on guitars with vintage origins (e.g., Styles 18, 21, 28, etc.), but uses closed-back tuners on more modern styles (e.g., Style 35, etc.), with some exceptions (e.g., open-back tuners on Style 40 and 41, which are modern-era variations of vintage styles). It does seem as if the super-duper premium tuners are open-back (Rodgers, Scheller, etc.).