I skied these as my park ski last season. I loved them, very fun to butter around and do presses. If you are looking for a rocker / camber hybrid ski to use in the park, I would look at the S3. It was marketed originally as an all mountain park ski, but in the past few years Rossi has marketed it as an all mountain ski, so less kids are considering it for park, which is their loss.
Flex: You cannot judge this ski by hand flexing it. The tips and tails have rubber sidewalls in them so if you run into something, your ski will not split in half. Therefore, when you try to handflex them they feel extremely soft because of the rubber. They are a medium flex throughout, fairly stiff behind the binding.
Durability: Rossi was one of the first, if not the first company to use the halfcap / mini cap / capped sidewall hybrid. It is very durable and resists topsheet chipping very well (this is cosmetic, I could personally care less but alot of people freak out about it). The not so good news: the edges are paper thin. If Rossi would switch to a thick edge, they would have the most durable skis on the market from my experience. I had edge cracks after a few days and pullouts by the end of March. I am missing a large quantity of edge on one ski (mostly due to a core shot along the edge) and about 1 cm on the other ski. The bases hold up decently, but are very fast if taken care of.
Mounting point: I remember this being a big dilemma when these skis came out. The sidecut is actually symmetric in between the points of contact with the rocker, but it is still around 7cm back from center. I mounted true center like any park skier would. The skis were very fun, but very different. I would only recommend this if you ski 100% park. There was almost no tip touching the snow in front of the binding, and a shit load of tail touching behind the binding. Pros-- very easy nose butters and nose presses. Cons-- the ski had a top speed limit before the tips gave out, carving wasn't it's specialty (which this ski does very well mounted at recommended).
All Mountain: Even with the center mount, these skis killed it in the trees and powder. The tip rocker is huge and I would float like crazy even in deep snow. Fairly nimble in the trees, very fun in the bumps, and decent on the groomers (again, due to mounting point for me). I saw more people skiing the S3 all over the mountain last year than any ski.
Sizing: These measure true to length. Because of the amount of rocker, I would suggest going longer if debating between sizes. If you are skiing rails only, then you could get away with the shorter size.
Overall, this is a great once quiver ski directed towards park oriented skiers. It is a great alternative to the Blend, Soul Rider, Bridge, Scimitar, Al Dente and other all mountain ~100 waist skis.
Got this ski to add due to its versatility. Originally from the east coast, my ski dreams have taken me to Colorado in search of deeper days. This ski handles all of the shittier days while not comprising its ability in the powder. A true one ski quiver.