I like a loose footed main. It really lets you increase the draft off the wind. Only problem is that you have to snug up the outhaul before you do a harbor furl, otherwise the sail just drops through the slot.
All your leech tension will come through the clew, and you have to deal with that. I played with different outhaul cars in the slotted boom, but none were satisfactory. Finally took an idea from the local go-fast boys and just put a dacron/velcro strap around the boom. Almost too easy.
My current main has the two upper battens full length. Upper one hangs up on the backstay now and then. Other than that, I'm happy with the sail.