Hi frederixx,
This mattress is made by Zinus/Sleep Revolution which is a Chinese manufacturer that makes a very wide range of mattresses under many different names. They are CertiPUR certified. In most cases they tend to use lower to mid quality 3 - 4 lb memory foams and I haven’t seen any that use 5 lb memory foam (although I have seen some that have been mis-listed as 5 lb) so I would be cautious with the 5 lb description.
The specs you provided only add up to 12" of thickness and the mattress is 14.5" thick so the specifics of 2.5" of the layers in the mattress are missing from the specs you listed and I would want to know what they were so that I could confirm there isn’t too much lower quality materials or any weak links in the mattress. There is already an inch of 3 lb memory foam so if there is another inch of lower quality materials in the upper layers then it would be outside of the guidelines here that I would suggest (no more than “about an inch or so of lower quality/density materials”).
According to the Costco site … the mattress includes …
4.5" overall of premium memory foam (which is probably the 1" 3 lb layer and the 3.5" 5 lb layer that they listed)
1.5" of Visco latex (there are no specifics about this in the information you listed)
7.5" polyfoam support core
Their specs include an additional 1.5" visco-latex layer compared to yours but they still only add up to 13.5" which is still 1" less than the thickness of the mattress.
Their description also doesn’t include any edge support but this wouldn’t affect the thickness of the mattress so this isn’t a discrepancy that would matter in terms of knowing the layers unless you listed the edge support in your description instead of the “visco-latex” layer.
There is also more about buying from Costco in post #4 here and there is more about the additional risk and uncertainty that can be involved in buying a mattress that has been compressed and shipped from China in post #6 here.
Assuming that you can confirm that there isn’t too much lower quality materials in the mattress (you would need to know the density of the visco-latex and any other missing layers or materials) and that the 5 lb density is correct and if you are confident that the mattress is a good match for you in terms of PPP (or are comfortable with trying it to find out because of Costco’s return policy) and you are also comfortable with the additional risk and uncertainty that can come with materials that have been compressed for longer periods of time during shipping from China … then if it compares well to your other finalists based on the parts of your personal value equation that are most important to you it would be worth considering.
Phoenix