Or like a very expensive Tempurpedic. All-foam mattresses aren’t all that inexpensive.
You are correct that you will not be able to easily return it once opened. They “inflate” to the size of a normal mattress and can’t be squished back without industrial vacuum equipment
I have one and love it. A couple bits of advice: thickness is important, as is the types of layers. 10" or less is going to generally be pretty firm. The 12"+ ones are generally going to be a bit softer.
The different layer compositions make a difference. The good ones will generally have at least 3-4" of memory foam and the rest being denser “support foam” or something. Speaking VERY broadly, the more memory foam the better.
If you decide to keep / try it, there’s a few things worth knowing:
They take a couple days to fully inflate. They usually say not to sleep on it for 2-3 days, although I’ve heard it’s fine if you do (but it may not be fully comfortable).
They take 2-3 weeks to complete degas. Until they do, your room will smell strongly of the chemicals used in the foam. I don’t find it actively unpleasant, but it is very noticeable early on. In my experience, the smell was entirely gone in a month.
You need a foundation or box spring that will support it. It needs a solid support under it every few inches.
They have a break-in period. I found it comfortable from day one, but moreso after a month or so.
I used to wake up achy, under-rested, and with back pain almost daily. Having a memory foam mattress has massively improved my sleep. I’m sure a high-end traditional mattress would have helped, but foam mattresses are incredible bang for the buck. I paid under $400 for it, and it’s massively, massively better than my last name-brand tradtional mattress (which cost at least $1000).