Hi EZ4HZ,
I have talked with Marc at Nature’s Sleep (not Nature’s Rest which is a different company) and he seemed to be very knowledgeable and transparent about the mattresses they make and I believe that he would give you accurate and reliable information about their mattresses that are sold through various retail stores.
4.6 lb memory foam is within a 10% spec tolerance of 5 lb memory foam so it wouldn’t be unusual to see it listed as a 5 lb memory foam. Foam densities are never exact from batch to batch.
I would also be aware that the prices at Nature’s Sleep are not “real” selling prices that most people would ever pay for their mattresses … they are just prices that are designed to make their retailers selling prices look better for consumers that aren’t as knowledgeable about how to make more meaningful comparisons between mattresses.
So I would confirm the specs of the mattress you are looking at with Nature’s sleep and if it does use memory foam that is within the guidelines here and if you you are confident that the mattress would be a good match for you in terms of PPP (or you have good options to return or exchange it if it isn’t) and you are comfortable with any additional uncertainty that is part of purchasing a mattress that is manufactured in China then it would certainly be worth considering as one of your finalists.
Phoenix