OK!
Before I start commenting, I need to put things back into the right context:this review is based solely on a PERSONAL appreciation. I've tried both the Helix and the Rebel 08 on very light wind (not possible to get planing, pure kite flying), and in powered up condition (20-25 knots). Now, main difference in the conditions, I tried the Helix on flat water whereas I was in waves with the Rebel. Both 12m2. Important to mention in this review, these days I'm around 55 kilos max (which has totally affected the way I hold on to my kites at their top end).
I really thought I was totally sold on the Helix after having flown it, but after flying the Rebel 08 yesterday, I've found myself really confused!
They're both fantastic kites, but a comparison will be really hard as it truly is comparing pears and apples!
They totally are different kites, and I reckon they will suit totally different types of riders.
In very light wind, the Helix shows a superb stability. No flapping, dropping off the sky. I would say that the Rebel's got less grunt on its low end, while still being lighter to stir in light conditions. However, was really stoked with the Rebel's 08 low end improvement compared to last year's: it definitely has more grunt and power in light conditions. Both fly beautifully, but their feel is really different. The Helix still feels like a 7 struts kite: more powerful but it did feel slightly heavier on the bar than the Rebel in light breeze. But in the same wind condition, the Helix was still getting me planing when I was struggling with the Rebel.
I'm no light wind fan any way, so let's go now to the real stuff!

Powered up, the Helix offer that magnificent grunt powerful kites do: huge pull, very reactive, constant power, and an amazing stability.
As I've said, I thought I was sold on the Helix until I tried the Rebel 08 yesterday, but important thing there: I have been a huge fan of the Rebel 07 and have flown it for months. Therefor, I'm a lot more used to handle the Rebel than the Helix. But yeah, flying the Rebel 08 yesterday was like meeting an old friend again, and I still think this kite is fantastic. The main thing that struck me right away was the turning speed: a lot less input is needed in the bar to get the kite to turn. The Rebel 08 turns ridiculous fast, it's a rocket! I believe the Helix can turn as fast, but it would require more bar input. The Rebel moves like a shooting star (definitely faster than last year's!)! Both kite just FEEL different. It's really hard to compare them cause it's like comparing a Ferrari and a Porche basically! 2 excellent kites, but with different acceleration, bar feel, way to move and behave up in the air.
The Rebel still shows its incredible stability, but as hard as it is to believe, I reckon the Sigma shape and the geo-tech on the Helix push the stability up in the air one step further....In the gustiest conditions, that kite just doesn't move the slightest bit. The Rebel is super stable as well (it was the most stable kite I had ever flown last year!), it stands up to its reputation, but it seemed to me that it was still more sensitive to unsteady wind than the Helix. The Helix is just amazing on this matter:it doesn't move at all.
Boost wise, they're different as well: different lift, different ways to throw the kite, different hang time... Jumping with the Rebel is a lot easier (to me, but that is only cause I've been flying this kite a lot more than the Helix): you don't even need to edge with the Rebel, just sheet in, zoom, gone! The jumps with the Helix are similar to the rhino's jumps: old school style, edge really hard and hold on!!! Super for fully loaded jumps. The rebel is more straightforward, the helix more radical... So there too, they're definitely different. The hang time is different, with the Rebel providing a faster lift (one gets pulled instantly), but letting you down much faster as well! The Helix with its 2 additional struts offers a lift thats more progressive, but the way down is much smoother. I do love the lift and gentle way down with the Sigma... As an hybrid, the Rebel still offers the lift of a C-kite (straight up!), while the Helix jumps much more like an SLE. In height, my judgment is biased due to the fact I'm so used to jump with the Rebel... So did go higher with the Rebel, but I'm fully aware this is only because I know how to work that kite. I really want to fly the Helix more to find out what I can get out of it, and I do not doubt I can achieve the same height with it... There again, different animals, it's all about how one communicates with them!

I've loved jumping with both, giving a big thumb up for the soft landings the Helix offers, and the immediate lift given by the Rebel.
So far, it's still all good for both, they just really behave differently. So really hard to prefer one to the other!
Now, in waves... That's where my crush went for the Rebel... I wouldn't have wanted to be on anything else than this kite yesterday. Lightening turning speed, instant depower, it is just the most PERFECT kite for wave riding!!! I ride hooked and strapped (I leave the cool stuffs for people with bigger arms than me

!), and I don't think I could have achieved such turning speed with the Helix... There again, let's not forget I'm used to the Rebel's behavior, and did not get the chance to play with the Helix in waves... I know JB loves it, so it's got to be just as good as waves are his favorite playground, but for someone much less experienced than him in surf, the Rebel seemed so easy to handle! Super forgiving, depowering in a flash, it just made everything easy. The Rebel has always been known for being a super forgiving kite, easy to handle. The Helix is a lot more radical, it's more aggressive, the Rebel has a softer temper, its versatile and more forgiving.
The Helix has that potential of a kite easy to use, but that will deliver the performance requested by the rider. Its potential is huge, and basically, this is the kind of kite that will just adjust to what it's been asked! The Rebel this year has this tiny bit of spice that certain riders (me included) thought it was lacking last year after riding it for months. This year's model has gained in personality and can now get to a similar feel to the Vegas.
The Helix seem to be supplying more grunt whereas the Rebel turned much faster.
The two main differences I came to highlight were the stability for the Helix (it doesn't get more steady than this in gusty wind!), the turning speed goes to the Rebel. I reckon for everything else, they're just too different...
Torch lovers will find all they ever loved about Naish kites into the sigma, with a massive increase of depower, an unbeatable stability, a relaunch even faster, and really really smooth handling with gorgeous hang time. the Helix is fantastic for hardcore riders, but it would be perfectly suitable for complete beginners as well: anyone can get out of that kite what he wants.
Rebel lovers will find a new model, with all the characteristic that made us love the Rebel 07, with an increased grunt on the low end for the 08 model (definitely pulling a lot more in light wind), even more depower (55kilos on 12m2 in 25 knots yesterday on a strapped surfboard and doing just fine!), increased turning speed, and still those crazy jumps and wonderful handling of gusts... It's the ultimate "life made easy" kite, with however more temper than last year's model. (and true, Cwamit, you don't need a 7m, I agree with Daz!).
Relaunch on both kites is easy as and super fast.... (but different as well as the kites do behave differently, the Helix relaunching like an SLE, when the Rebel still swings back into the edge of the window before going back up)
I'm not sure this review helps, as I recognize myself I now really don't know which one to go for!!!
I love both, it's going to be really hard to make my mind up (it just means the Demo shelf is going to live in my car, basically, lol!!!)
The way I see it, people need to FLY these kites and work out which one suits them better, but it mainly comes down to SLE or 5th line, how aggressively one wants to ride and what main use one wants to do of their kite...
I'm really curious to know how heavier riders felt about these two kites as a 90 kilos rider would have a totally different appreciation... Anyone???