Hero,

I've seen in-mast mains with roaches using vertical battens. I don't
know anything about them.

My first thought was about controlling twist? I've never discussed this
with someone who has used them.

There is a Schooner rigged boat out of Friday Harbor out here, who has
converted all his sails to wind-ups and seems very happy. They aren't
in mast furling. He has set up furlers behind the masts. He has control
of all his sails from the cockpit.

He does mostly single handing and it gives him a lot of options on sail
combinations

Ole Thom