The friction compounds they offer are Organic, Kevlar, Ceramic, and Sintered Iron. They no longer offer Feramic, or Organic/feramic clutches. I have had every clutch Valair offers for the ZF5, and all of them had very easy clutch pedals. The only one that is a little stiffer is my 3850lbs Sintered Iron double disk in my puller. The sprung hub organic dual disk I'm running in my daily driver has an easier pedal than stock.
Absolutely their double disk is a great option. However I will say, on some ZF trannys you have to shave down some webbing inside the bellhousing. But a grinder and flap wheel makes short work of that in about 2 minutes.
What sets them apart from the others? Customer service after the sale first and foremost. And price is a huge hitter. At any given time you can call up there for any questions and they will be more than happy to talk to you. Dan, Gary, JD, and all the guys up there are gear heads just like us. We all sled pull together actually. They will bend over backwards for their customers and friends. That's what sets them apart.
As far as the warranty, I couldn't tell you. I never had to think about it. You might say, well, how come you had every clutch they offer. That's because I helped Dan design and R&R the double disk clutches they offer for the ZF5. It took several tries to get it perfect the way Dan wanted it. So every time we pulled the tranny for another shot at getting the dual disk dead on, I just installed a different single disk when we were done. At least untill the DD was finished, from then on I've run dual disks in my trucks. I would still be running the ceramic dual disk, but it was jumpy for pulling heavy, so Dan built this sprung hub dual disk. And I'm telling you it's the cat's whiskers.
The bottom line is I think if you give them as shot, you'd never go anywhere else for clutches. But everyone has their personal preference. I just prefer Valair.