I didn't read the website but here's my thoughts on kits anyway. They don't include ground prep, and most don't include wiring/plumbing/flooring/insulation, etc etc etc.
I almost went for one, and the guy who ended up building my house did the math and proved to me that the kit company was charging a premium for lumber.
I did much better by sending materials lists to all the
local suppliers and taking best prices.
If it's a "to lock up" kit, basically the home hasn't even been started yet- it's just roughed in. There's a lot more to a home than the walls/roof.