I am considering returning our Sloom King XL.
It is better than our previous bed, and having options is great, but on the firmer options the softer mattress sections are on the bottom so it can "dent" a bit during the night and my ass ends up lying in a slight hole.
It is a "known issue" for me. I have had a pocketed coil mattress which I returned after 2 nights for the same reason, and our previous (way too soft) bed did it as well, although to a much worse extent.
If you sleep on the medium or soft sides, it shouldn't be an issue. It is also great if you and your partner like different firmness.
It could in theory be fixed by placing a plank between the firmness sections, but do I really want to do that with my R11K mattress to get what I want?
I read on their FB page that they have about 2% return rate, so more people like them than not.
I am a 87kg, 1.9m side sleeper who have always preferred firm mattresses, for reference.