The XP version has a panel-mount power module, so unless you're an exceptionally well-off 16-year-old with your own aircraft, the XL will be the version for you.
Can't say they appeal to me however. For that sort of money I'd opt for the more modern Lighspeed Zulu.
Not that I ever had that sort of money to splash out on a headset when I was 16... that must be some paper round you're on.