I agree that the Hullo does stay cooler than normal pillows, which is nice. It’s particularly important as this means it doesn’t require flipping, and you basically can’t flip it. At least not easily while laying down.
My problem was that even after a few weeks sleeping on it it still constantly woke me up because of how loud it is. It isn’t so loud as to wake up the person next to you, but your ears are right up on it, and while I assumed I’d eventually “get used to it”, even after a few weeks I still wasn’t sleeping well on it. I’d have returned it, but it’s really quite heavy, and I suspect the shipping cost would have made it not worth it.
It does seem well made, and I like the product in theory. I doubt most people will find it too loud, but I did. I’ve just been using it when I lay on the couch.