I had single-hose both when I lived in USA and now, and didn't have any issues with it cooling down the room I wanted to have cooled down. My bar is "survival of my pets" because rabbits supposedly can't handle more than 25C. Their room stayed well below that temperature both in USA (Seattle suburbs, west-facing in a house that wasn't insulated) and now in Portugal.

Ive seen a few single hose AC units that worked okay. I still don't understand why they exist though. The window installment at its minimum span is still putting the ends quite far apart and would increase efficiency.