Replying to Banshee Bungee worth it? what length?

Hey i know there have been threads about banshee but none with any helpful info. I was looking at getting one through the deals today and was looking at the 15 ft. Just wanted to know peoples experiences with them and if the 15 is gonna give me enough speed? looking to do a good amount of urban; rails, jumps, whatever. Obviously the 30 foot would gvie me more speed jus not that keen on blowing the extra 100 bucks.