Hi, usually I only read here and post mainly about SUP, but having some 3 battens and sailed a lot with them, so I think my opinion might be interested for those who thinking about 3 battens.
First to be clear I,m back riding for Hot in Holland after a 2year on custom sails. but always try to be as unbiased as possible and not to act as a fanboy.
When I ordered my sails I didnt include the KS3 as i didnt believe the Hype. I associated 3 battens with lots of maneuvrability, light and lack of low end as well poor high-end (sailed a different brand 3 batten that i,m not gonna name here) and was pretty sceptical about it.
I oredered 4 and 5 battens and they gently refused my order till I at least tried the KS3.
Got a demo and man i,m glad they did :).
The magic ISNT that it has just 3 battens, its a complete different sail concept.
First if all, It got the S foot batten that put a lot of pressure in the bottom of the sail. That and the wrinkles in the luffpanel fill in a deep belly when the wind kicks in and depower when you sheet out. This gives a forward placed profile that has a lot of range trimmed over the OH from full hanging against the boom till really really flat and stable all the time, that and that you have lots of space under the boom for you legs makes it very maneuverable.
This could be made with a 4 batten sail as well, but it is stable enough with 3 so why ad a batten extra?
The benefit of a batten less is simple: battens help with shaping, but also slowing down the reaction of the sailcloth. less battens means a more reactive sail, ooh and having a batten+ the construction to fix it less saves indeed weight.
I got a KS3 now in 5.2 4.6 4.0 and a 5 batten Firelight 6.0 5.3 and 3.4. As soon as there come a 5.8KS3 its gonna be mine

The 5.3 FL is actually lighter as my 5.2 KS3...but due the less batten/easier to breath cloth on the KS3, the KS3 FEELS lighter and quicker to me.
Of course you probablly all think, teamriders bullock, but to me the sail felt a bit like the first twins after the decades of single fins, it just allows you to sail differently.
That doesn't mean better, because a 5batten that is less reactive can feel easier more sedate but i haven,t sailed one (and I really like to try other peoples gear)that felt so responsive and reactive like my KS3.
Its really hard to understand the whole thing till you actually tried it.