* will there be enough meat left on the string after trimming to refit old strings?
Probably not - but that's true with all locking tuners. Why do you need to refit old strings anyway, you skinflint? (

) You could always leave the ends untrimmed if it's an issue.
* not certain which way to turn the tuner while its locking - the tuning post doesn't turn during this phase
The same way you'd turn normal tuners!
* not convinced it will be faster to lightning fast change strings at a gig vs a normal tuner
That depends how small you make the hole in the post before inserting the string - if you (or your highly-paid guitar tech) can get that down to a fine art, the mechanism locks very quickly. Probably difficult in backstage lighting conditions though - I admit the Sperzel/Schaller design is quicker/easier in that respect. But you can't get them in vintage styles.
Sorry, I'm being defensive. I love my Gotohs! :)
I must admit I have sometimes forgotten which way to turn the
heads of the tuners to loosen them (the ones on the plain strings have to tighten anti-anticlockwise for the design to work, which is counter-intuitive). I damaged the chrome plating on a couple by tightening them when I was thought I was loosening them.