If you plan on keeping the Jeep that long and don't plan on modifications then I would definitely buy one.
I have not purchased through that site, but it shouldn't matter. They are just selling an official Chrysler Service Contract at a reduced price. Should be something like $2000 from them instead of something like $2800 if you called Chrysler directly for a lifetime warranty.
I have the 6 year / 75K maxcare on my Liberty. I figure beyond that I will have switched out much of what is covered anyway
Good luck!