hellbents are amazing in the park, ive only taken a couple runs on them through the park, but i ski my ep pro's in the park all the time which are fatter and quite a bit softer.
sure you cant get super techy and do multiple switchups and pretzels and all that, but why would you with those skis? actually i can 270 onto down rails with my ep's. i find that any more than a 450, or two switchups and they just dont work that well. but if your skiing rockered skis in the park theres no reason why you would even want to get technical.
as for jumps, ive hit 60 footers with mine, even landed pretty far backseat, as long as you stay somewhat centered they will be just as good as any other ski. they are more fun than any park ski ive ever ridden by far.
you can butter anything, butter on and off rails, butter off the lips of smaller jumps, hold your butters for like 10 seconds, press rails like crazy, etc....
it totally changes how you can ski the park, instead of looking at a jump and thinking "how big of a spin can i do?" you look at it and say "how can i hit this in a totally different way?" like using the side of the jump as a take off, doing butter combo's etc...
not being able to do super fast spins, but being able to press, pop and butter like crazy on anything totally changes park. if anything id say they are the best park skis ive ever ridden.
oh and the idea that rockered skis dont have pop is crazy, my ep's have more pop than any park ski ive ever owned.
