That’s a good point about the Arfs but they only have one set of fins, and they can be interchanged, but the ah - hem “Screw Machine” is the only one I can think of so far that made it a feature, meant to be flown, then switched out for different shaped fins. The Mix and Match instructions say you have to use fins all of the same shape on one rocket, and glue them on. You could definitely do it with the Mix and Match, Estes missed the boat on that one, maybe John had one go sideways and said “Yep, glue ‘em”.