On my 30'' ULDB (1995 vintage), I switched to a full upper batten last summer to fix a "hinging" problem with the long top batten. This helped to get another season out of the sail, but caused problems with the backstay...another step to take while tacking. I definitely would not want full battens on the lower three. However, lately, I have been sailing on a 43'' offshore racing trimaran, where all battens are full, and on this boat full battens are a real necessity. By design, there is no backstay to deal with as the boom extends aft of the stern. There are some very hefty running backstays though.