A local dealer in So Cal was adamant that the sail is just a 'downwind' sail and you really can't tack or sail upwind unless you go with the AI.
What a bunch of baloney! It never ceases to amaze me how little some Hobie dealers know about their products. Obviously some of them don't have a clue about sailing a Mirage Drive yak, and/or have never done it. That is the beauty of the Hobie sail kit over some other kayak add-on sailing products out there. You can sail (and tack) beautifully both upwind and downwind with the Hobie Mirage sail kit--either the BigA/AI model or the "standard" Hobie sail kit on the Outback, Sport, Revo, etc.
Of course, the Mirage Drive does double duty in such cases (non-BigA or AI that both have a separate daggerboard). First, it is very useful in coming about. Second, it is important to keep the fins fully extended so they can act as a centerboard/daggerboard to cut down on side-slipping when sailing or tacking. Try it, you'll like it! Oh yeah, a hearty welcome to the Hobie site--great folks and great info here.