Dude, it sounds awesome. I'm getting me one of those. High for 5 hours? Amazing. I'm only ever high for 5 hours if I've been mixing bongs, pipes and blunts. And it has to be chronic. I used to be a daily smoker up until 2 months ago. I try to keep it to once a week now. So much more gratifying, satisfying and cheaper!!!
But it's really a couple-times-a-year thing, so don't get too excited, and you have to get some good shit and take a huge hit (like a 2 liter bottle). Though pretty much all of my friends say that the highest they've been was also with a gravity bong, so it probably won't dissapoint.