I bought a portable a couple of years ago, it's by a heavily curtained window in the smallest bedroom so the there's a gap for the pipe, and I've done my best to cover that gap so the hot air escapes. On full blast 16c for 15 mins it does cool the room down markedly, when used after sunset on a still, very warm muggy evening. I notice it walking in!
However it's too noisy and cost-consuming to leave on all night, so if I'm not asleep (on my camp bed!) quickly the room soon gets back to greenhouse levels even at night with the window/curtain closed.
Seriously thinking, over the winter, installing a proper unit, probably cost well over £1000. But it's a room I can use for a bed, PC, telly etc to keep me cool and entertained on hot evenings.