Replying to Banshee Bungee: 10ft or 20ft?

I've been planning to buy a banshee bungee, because i don't have a drop in and most of the handrails we have here requirers one. And also, how much speed can it give on flat ground? Is it able to built jumps on flat and get good air? Is 10 ft enough or do I need 20 ft on the jumps and long flat rails? Any experience of using it, anyone? Sending videos of using both sizes for comparing them would be useful, thanks.
+K for help.