Hi worknman,
It seems like you don’t like answers that I have used on other occasions to answer comments or questions that have been asked many times before and you would prefer your very own “unique” reply? If I change a word or two would you feel a little better?
You also forgot the second part of the reply I usually use for questions about online mattresses that ask about which firmness level to choose or how a mattress “feels” which starts with …
but I won’t “bore” you with the rest of the reply since it doesn’t apply to your question anyway.
There is also a common reply I use when people ask about firmness levels as well that starts with …
But once again it isn’t connected with what you are asking so I won’t “bore you” with the rest of this reply either.
I suppose I could even use a “shotgun” approach and include every one the hundreds of reference posts I often use to answer common questions and just hope that one or more of them applied to you.
Finally I suppose I could just leave your questions unanswered since you appear to enjoy criticism or sarcasm more than gratitude and let you find your own answers by searching the forum or trying to find other reliable and factual sources of information.
In this case though you are asking about the quality/density and durability of the materials so I don’t need to “bust out” that “canned” reply and you don’t need any “consensus feedback” since assessing the durability of a mattress is just a matter of knowing the density of the memory foam and polyfoam in the mattress and comparing them to the quality/durability guidelines here (sorry for linking you to guidelines that I didn’t write especially for you).
I should also mention that this information is available on their site as well (with the exception of the density of the 3" 1.8 lb hole punched polyfoam in ther luxury firm mattress).
The soft version of the Nest Alexander Signature uses …
1.5" polyfoam quilted to the cover
2" 4 lb gel memory foam
2" 4 lb memory foam
3" 1.8 lb hole punched polyfoam
4" 1.8 lb polyfoam.
The medium version uses …
2" polyfoam quilted to the cover
4" 4 lb gel memory foam
1" 4 lb memory foam
2" 1.8 lb hole punched polyfoam
4" 1.8 lb polyfoam
The luxury firm version uses …
1.5" polyfoam quilted to the cover
2" 4 lb gel memory foam
3" 1.8 lb hole punched polyfoam
4" 1.8 lb polyfoam.
All of these are good quality materials that would be suitable for more average weight ranges but I would be cautious for those that are in higher weight/BMI ranges (a BMI of 30 or more).
The medium version also uses a little thicker 2" quilting layer and I would normally suggest no more than “about an inch or so” of lower quality/density layers in a mattress and once there is about 2" or more of lower quality/density foam (less than 1.8 lb density for polyfoam in a one sided mattress) or “unknown” materials in the upper layers of a mattress then the odds of premature foam softening and breakdown would be a little higher.
I hope that this “satisfies” your criteria for forum answers that you consider to be “appropriate” 
Phoenix
PS: I sure hope that nobody else asks the same question because I might just feel “compelled” to link them to this post instead of writing a new and “unique” reply.