Hello - I just joint here looking out for the new redback - saw a prototyp shown at a freestyle event in the Netherlands an looks like it would be the best next fit for my daughter.
Joining the discussion on sail comparisons: My sons is riding the xs3 in 3 and 3,6 and the S1 in 4,4
The S1 in my opinion requires an absolute minimum size of 140cm bodyheight. under that the boom can't be adjusted within reach (below chin). My son is 144cm now, can adjust the boom comfortably, but the sail shape is not optimum for this very lowest position. The xs3s he is adjusting in mid position and that looks fine. Should be same with the redback in comparable sizes.
I don't like sails for the kids with long booms as you often find with special kid sets. My kids are very keen on freestyle and even the first tricks work much better if you don't have to handle over a long boom. And kids boards - especially my sons kids flare freestyle board - and also the beginner kids boards with centerfins react so easily that you don't need broad sail shapes.
One question to you
@Gestalt; do you own the xs 3 as a set? I think the xs3 boom is missshaped: the plastic part that holds the trim cord at the tip of the boom is on top (instead of on the outside) and if you trimm it properly, the end it does not fit into the cut out edge. you have to adjust the boom way longer than necessary or you force the corner of the sail to bent which certainly damages the sail within some time. Happens on both sizes and as I said in mid position Same with S1 (even worse) when you use the xs3 boom.
I don't know if there is that much difference between redback and xs3 - according to the data sheets its heavier than the xs3 (in the small sizes even 200g bigger sizes even more but which is due to the additional batten). The forth batten which comes 3m and over is the main advantage I guess, as Gestalt mentioned with stability. - compared to the xs3.
-compared to the S1 I think price is the only advantage if you are tall enough, but I think for (most) adult body sizes I would go for an older S1 or even S1 pro which you should even get cheaper. xs3 seems best choice for lightness as for kids is useful.
S1 is not much heavier than redback. (e.g. S1=2,7kg in 4,4 and redback=2,5kg in 4,2 (4,4 does not exist). S1 pro is even lighter.