Bart,

I use a loose footed main. I like it because I can carry the shape of
the sail all the way to the foot of the sail. I had used a shelf with my
other main and thought that was the way to go but my present sail is
completely free and I"m damn if I don't like it better. I do believe it
is faster and that is probably because of the ease in shaping the sail.
A bonus is access to both sides of the boom from the top of the boom

Adding a shelf is easy. Adding a bolt rope footed main is a different
ball game, I do believe