I have a pair of Outfitter tandems and have the sail kits. On a reach closer than abeam, I can't get a decent sail shape regardless of batten tightness. The sail tends to "bunch up" right where "Hobie" is written on it. If I raise the sheet off the aft deck, sail shape improves. It almost seems like the proper attachment point for the sheet to the aft deck should be about a foot behind the kayak to get decent sail shape.
In spite of this, I do enjoy using the sail and can still reach much closer than I would have ever guessed. The width and stability of the Outfitter, combined with the small sail and flexible mast, makes it possible to carry full sail even in quite high winds. I have had several long runs with one of my boys up front (8 year old), and my wife and the other boy (10 years old) being towed behind in the other Outfitter, maintaining 3+ MPH under single sail alone. The sail, combined with the pedals, has increased our average family outing range from 5 or 6 miles in paddle kayaks to 11 or 12 miles now which is great! That should go even higher once my wife is comfortable sailing herself.