A portable with two hoses would be better than the one hose version. But when I bought mine, there were no two hose versions at the big box store.
And you're right, that the available solutions for this, while highly imaginative, aren't much good. If you did not make a solid adapter, you might be doing something like this.
I've seen adapters before, made from a sheet of ply. The sheet of ply, intended to fill the window opening.
My apartment buildings in the past, had full balconies, so if you wanted to fit a window air conditioner on those, the unit would not be traveling all the way to the ground if it came loose. Still, the lease agreement could have a term that "only management could install AC and there is a fixed price for install". And they would have an adapter picked out for the task.
Some apartment buildings have central air for the entire building - the only trouble with that, is ventilation noise. Buildings like that do not have very good noise control on their ventilation. A buddy at work showed me his "deluxe apartment", and the first thing I noticed was the ventilation noise. However, at least the apartment unit was cool and no complaint about temperature in the unit. The apartments I rented, had no building ventilation, and you would open a window if you wanted fresh air. The bath would have a vent fan and a pipe ran to the building exterior for venting shower moisture.
But the apartments without balcony, I would want the management fitting a unit, as the opportunities for mischief are much greater in that case.
And someone in another group, just fitted two window air conditioners... and hurt his back. This is not a task we particularly look forward to, fitting air conditioners. His was apparently only 45 pounds weight per unit, but he was twisting at the time when his back went out. And when I've put my back out, it was the same thing, trying to work while rotated ninety degrees to the load.
Paul