I usually set too many eggs to hand turn. So I use a turner from days 1 - 18, then flat.Twenty years ago I had a turner. The first time I used it, I left it in the bator turned off at lock down. Chicks hatched. I didn't like seeing those poor chicks scrambling over that turner! Like a big obstacle course for them. They all made it.
The turner broke soon after that and I chucked it. I've hatched flat all 21 days and in the carton all twenty one days. I always got chicks.
This current hatch they remained in the carton for seventeen and I put them flat for lock down and hatch. Going to find out what happens. No matter which way I ever did it, chicks happened.
Now with Goose eggs, supposedly they have to be laid flat and hand turned. I have an automatic turner in my cabinet incubator, and eggs can be laid on their sides while being turned. Neat feature. Not sure how they don't roll all over though...?