Hi paddyb,
You can see my comments about Casper and the materials inside it in post #2 here in the simplified choice topic and a forum search on Casper (you can just click the link) will bring up many more comments and feedback about them as well.
I’m not sure if you are referring to a specific mattress or to mattresses that are shipped in a box in general (which would be too broad a question for me to answer because there are so many of them that are different from each other).
I can’t speak to how any mattress will “feel” for someone else but my thoughts about the quality and durability of any mattress would depend entirely on the type and quality of the materials and components inside it regardless of the name of the manufacturer on the label.
Phoenix