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He’s specifically complaining about single-hose portables. I wouldn’t say that single-hose portables don’t work, but they are substantially less-efficient than dual-hose portables. If you’re getting a portable, there are very few scenarios where it’s a good idea to get a single-hose portable. Unfortunately, single-hose portables are slightly-cheaper and simpler than dual-hose portables, and the great majority of portables on Amazon are single-hose.

Single-hose portables suck air from inside your house, heat it up by transferring heat from air inside the house, and blow the hot exhaust air out the hose. The problem is that because they have no intake — they intake the air for exhaust from inside the house — and thus create negative pressure in your house. This means that hot air from outside is sucked into the house, to equalize the pressure.

Dual-hose portables pull air in from the outside, heat it up with air transferred from indoors air, and then blow it back out to the outside, so they don’t have this problem.

They do leak a little more heat and have more noise in the inside than window units, but they don’t have the glaring problem that single-hose portables suffer from.

Note that this isn’t a new problem. Many people in the past have used fireplaces for heating. They create the same problem, just for cold air from outside instead of hot air — they send exhaust hot air up the chimney. That causes cold air to be drawn into the house. Doesn’t mean that fireplaces are non-functional as heating systems. Just that they’re less-efficient than they would be if they didn’t exhaust interior air.