Personally, I don't like having neighbours, I like nature, I don't mind living small. Such a house would allow me to put more of my resources in land. Then if I need more room for stuff I can build that myself (stuff requires less isolation and there are less strict rules for it in my country, etc).

Pretty sure you'll still need a concrete foundation, or else the house will slowly drift away. But plumbing is probably the hardest/most expensive thing about it.

I've said this elsewhere in the thread, but putting a small/tiny house on a trailer is a good option and won't drift away (at least not in the foreseeable future since it's on wheels with jacks to keep it in place). I think we've reached a point with composting toilets and grey water where plumbing is not that hard, nor expensive. Yes, you still need a water source, but running the actual plumbing lines is low-cost and as long as you're willing to use a composting toilet (no plumbing lines for that obviously) and make use of your grey water in/around your property (which in a lot of the western US should be the norm instead of the exception) it's pretty reasonable. Does require a different way of thinking about things and in a lot of urban areas the "state" might have regulations that prohibit some of these things.

A single wide mobile home, which is x2-3 as big as this, is cheaper than this costs. And, in most parts of the country, you can buy a full home with land for less than this costs installed.

Their advantage seems to be how quickly they can deliver and install them. Digging into their website, it sounds like they're targeting temporary housing for natural disasters, etc. which makes sense.