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It's on my shopping list.
There's not a huge number of units that just require a bit a of ducting through walls - most are massive boxes that go through the entire wall, and would need studs to be cut & headers / footers put in.
And ain't nobody got time for that.
NotThamesWater-
I've been looking into this a bit more and am leaning towards the split variety. Not sure what you mean about a massive box in the wall - the one I'm looking at only needs a single hole that's definitely smaller than the ones on the inside only one you posted. Downside is an ugly thing on the outside obviously, but can always put it on the back out of sight. Also needs to be installed by a professional. Upside is a much smaller unit on the inside which really appeals to me. Also cheaper
For reference: https://www.appliancesdirect.co.uk/p/iqool12plus/electriq-iqool12plus-air-conditioner-air-conditioner
Hovis
Only just saw this. Did you go for it? I didn't know there were units that didn't need the ugly external part, I need to do some research.