Hi equestride,
Unfortunately your experience is fairly “typical” and it’s not unusual that the members here that have spent more than a couple of hours on the site will generally know more meaningful information about mattresses than most of the salespeople that sell them in the mainstream industry.
Yes it would feel different but how it will feel different would depend in the specifics of each mattress you are comparing along with the body type, sleeping positions, and individual preferences of different people. Each person can have very different perceptions about how any two mattresses compare in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences). There is more about “matching” two mattresses in post #9 here. There is also some general information about the differences between a latex/polyfoam hybrid mattress and an all latex mattress in post #2 here but this is only generic because there are hundreds of versions of both types of mattresses that would feel very different from each other.
The information you listed is also very incomplete so it’s not really possible to make any meaningful comments about any mattress until you know the type and quality of all the materials and components inside it. In the case of the Restonic mattresses you are looking at you would need to have the retailer call the factory to find out the information in this article if they don’t have it available. If they either can’t or won’t find out the information you need to make an informed choice then I would pass the mattress by because a “blind purchase” is much too risky and has a very high chance of buyers remorse much too quickly after a purchase.
I also wouldn’t assume that any mattress that a salesperson calls a latex mattress really is because there may only be a very thin layer of latex inside it mixed in with other materials that could make the latex mostly meaningless.
Again there is no way to answer this or even guess at an answer until you know the specifics of what is inside the mattress.
As you also mentioned … Spring View is the only store out of the options I listed whose website indicates that they carry all latex mattresses with their Pure Latex Bliss line (although PLB also makes latex hybrid mattresses). You can see the specs for the PLB all latex mattresses in post #2 here.
Phoenix