Nice video Markus! For those who don't know, Pixel lives in Germany. He's got all kind of different riding places over there!
I guess I'm a little late chiming in here but to address what seems to be the biggest question I will just give you my half. I like the idea of progressive springs but I like dual-rate better. The first reason that comes to mind is there is adjustability with dual rate where there is none w/ progressive. We offer standard rates provided with our medium and heavy rate kits which we've determined, after a lot of testing, to be the best "average" combo's for two generalized groups of RZR S owners. After that, we also offer custom combinations we can custom tailor for you over the phone typically. With progressive springs, you get what you get. We are also offering a bit of an exchange program where if you decide you want something different out of your ride we can exchange your long springs for new ones for a much lower price than buying a whole new kit again and we give you 50% back for the old springs when you ship them back to us.
The other advantage with dual rate springs is when they shift rates it's a 100% positive engagement where with progressives the entire coil is always along for the ride. The advantage is the dual-rates can be a little more consistant in their handling characteristics. We've been getting a lot of feedback from customers saying our dual rate kits are substantially more stable than stock springs and even progressives while cornering.
The delrin spacers provided with the kits have different length I.D. shoulders on them which allows you to flip them over and "tune" the timing a little for when the secondary rate engages.
One last advantage I can thing of of the top of my head is the RZR S dual rate kits we sell now stack up to 14" long. This is a HUGE advantage over anything else out there. This helps the shock and everything about it's stroke and the springs life expectancy. The I.D. of the springs is very tight to the body due to this small of a spring size but everything seems to be working fine with this setup.