Our resort in NH just got one installed. It's $15 for four jumps, but your first jump you are required to straight air, so you're really paying for 3 jumps where you can actually practice tricks. Rates will probably vary though.
I coach younger kids and we were on it all Sunday morning - its super fun. Backflips are easy enough once you figure out to pop off the lip. I think these things are great for learning how to do bigger spins and then incorporating corks into the rotations.
You CAN get hurt on these things. Our mountain has seen mostly collarbone fractures from people landing on their upper neck/shoulder. There was a spiral tibia fracture yesterday - skier tried to spin big and landed - his foot and knee stopped spinning but his torso kept going. Snap. Ouch.
Be sure to get a tutorial from someone in the know about these things before going really big. There is less risk than a normal jump but it is not 100% safe.
Safety aside - super fun. Definitely go do it!!