As a structural engineer I feel compelled to tell you that it may not simply be a matter of cutting a hole in your ceiling and installing this lift. The "Framing Specs" section of the first product's website is a joke and could get someone killed. I love their:
No shit, really? You mean most attics aren't designed to store much of anything?
So I guess what I'm really trying to say is that don't ignore the complexity involved with safely installing the lift. I'd recommend consulting a professional engineer, not a contractor (no offense to Steve), before doing anything like this. And for the love of Pete, please don't buy a commercial scissor lift and try to use it in your house.