I'll grant you the Thule looks the best of all of them, however for pure functionality and cost, the Sears XCargo Box is a better deal. I studied all of them, and as for going to the beach with the kids, the Sears box holds all the bulky crap associated with the beach and kids.
I drove around 80 mph for 6 hours, nothing really noticeable to complain about.
I'd rather rent one to be honest, cause now I have to store the damn thing!