CrankyCarrot

You can mod the portable ones to be basically as efficient as the proper units by installing a second hose over the hot side intake and adding that to your window seal kit so there are two hoses. The only inefficiency left then is the exhaust hose acting as a bit of a radiator but especially if you place it by the window and keep the hose short, that's not really that big of a deal.

They are bloody noisy though. There are some properly split window units finally coming onto the European market that will be better for that but still very expensive

There is not a single one in stock in the entire UK, plus dual hose versions are basically non existent here too.