They're talking about window units, not heat pump systems or central air. It's a complete AC that sits in your window. It can't cool a very large space (even in apartments people may have more than one), but it's cheap and easy to install (and equally easy to remove). It might be unsightly on a house, but a lot of that is probably just cultural norms. They're very common in NYC, where a lot of housing was built before central air became the default.

I think you are thinking of mini splits, and not what americans would call a window unit. I got my window unit for $100 off craigslist and put it in myself without needing any tools.

Right. I only know one version of air conditioning and have never really seen anything other than what you call a mini split.

That's not what a window AC unit is.

And yes, it's true they're kinda ugly, but it's better than baking in the heat.