Hi hickoryboy,
Both polyfoam and latex come in a wide range of softness and firmness levels so this has little to do with the differences between the two materials.
The main differences between the two materials (I’m assuming here that by "softer foam you mean polyfoam rather than memory foam) is that latex is more “point elastic” which means it can shape itself to the body profile better than polyfoam (more pressure relieving), it is more “supportive” than polyfoam (it has a higher compression modulus which means it does a better job of holding up the heavier parts of the body), it is made from fewer chemicals than polyfoam (especially the natural versions of latex), it is more open celled, breathable, and cooler than most polyfoam, it has a more resilient and responsive feel than polyfoam, and it is more durable than most polyfoam. Of course as you mentioned … it is also a more costly material than polyfoam but it is the “standard” for fast response foams that polyfoam manufacturers try to duplicate. If by “softer foam” you mean memory foam then the difference is even more dramatic because memory foam is a slow response material and has completely properties than either polyfoam or latex.
There is more about the different materials that are used in both comfort layers here and in support cores here and there is more information yet about the different types of latex in this article.
As with any mattress … the materials in the mattress means much more than the brand. They are CertiPur certified which means that they have been tested for offgassing and harmful chemicals which is important with mattresses that are imported from China but like with any mattress, I would want to know the specific information about the density of the memory foam and polyfoam that is in any mattresses you are considering. This is the only way to know their quality and value. As you can see from post #2 here (and various online sources as well) … the Visco Heir uses sub 4 lb memory foam which is low quality memory foam and lower than I would generally recommend looking at unless price (they are available in the $600 range for a queen) is a much more important factor than durability. I would also caution that only testing a mattress for a subjective sense of “comfort” that you feel in a showroom can lead to the purchase of a mattress that may not be appropriate for you and it’s much more effective to test a mattress more objectively for your specific needs and preferences or what I call PPP (Pressure relief, Posture and alignment, and the Personal preferences that are listed in post #2 here).
Comparing lower quality memory foam with latex is not an “apples to apples” comparison because memory foam is a completely different material than latex and the memory foam in question is low quality so it can’t even really be compared to higher quality memory foam mattresses. Latex is a more durable material than even high quality memory foam and iof course is much more durable than low quality memory foam. The choice between memory foam and latex as a whole is really about personal preference and which one better suits your needs and preferences. I would first decide which material you prefer (fast response vs slow response) and then choose the best value in the material you prefer. I would personally first choose the type of materials that I preferred and then choose the best quality/value in that type of mattress that was available. Of course an all latex mattress is more expensive but there are also latex hybrids available which use several inches of latex over polyfoam (just like memory foam mattresses including the Visco Heir are really hybrids with several inches of memory foam over a polyfoam base).
Buying “any mattress” because of price first can easily lead to regret over time because the quality of your sleep is most important and your body won’t feel the price you paid (until the foam softens and degrades) … it will only feel the pressure relief, support/alignment, and the other preferences that are important to you and over time these will be much more important to you than the price you paid.
Phoenix