You can see some comments about them here that were based on a conversation I had with them that was also the reason they were added to the mattress component post here.
The quality of the materials is certainly good yes. As Novosbed also mentioned … the base layer may be a bit of “overkill” because with HD polyfoam there is really little benefit in using a support layer that has higher density than about 2.0 - 2.2lbs. If the base layer is HR polyfoam on the other hand (which has a different chemical formulation than HD polyfoam) then it will have better specs and higher performance than HD polyfoam but they would need to confirm that it was HR rather than conventional HD polyfoam (HR has a compression modulus of 2.4 or higher and resilience of 6t0% or greater in addition to a density of 2.5 or higher).
Memory foam is not used in a support layer because it is too soft (and gets softer over the course of the night as well as in response to heat and humidity) and is only used in the comfort or transition layers.
The reason that many manufacturers use a combination of different memory foam densities is that they create different “feels” and respond and perform differently. Generally lower density memory foams are a little more responsive, a little less temperature sensitive, and a little more breathable. Higher densities can also take a little longer to respond to temperature and take on the shape of the body so they can feel firmer for some people than lower density foam. I would also keep in mind though that there are many varieties of all densities of memory foam so this is just a generalization.
Using different foam types, foam densities, layer thicknesses, and layering combinations in a mattress is how different designs are created that can be more or less suitable for different body types, sleeping styles, and preferences. There is no “one type fits all” in in terms of materials or design in the mattress world.
Each manufacturer can have their own thoughts and ideas about mattress construction and design so you may find a wide range of different opinions about everything connected with mattresses. This generally isn’t a matter of one is “wrong” and one is “right” but just differences of opinion based on different ideas and beliefs about mattress construction and different preferences and experiences with various mattress designs. Sometimes it can also be connected to what they sell or have available.
The bottom line is always …
Does it match my needs and preferences in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences)?
Does it use durable materials that won’t soften and break down too quickly?
Is it good value compared to other mattresses that have a similar design and use similar materials?
Finally I would be cautious about becoming your own mattress designer instead of working with a manufacturer that already knows what you would otherwise need to learn. It can certainly be a lot of fun and can even be a rewarding experience but it can also involve a great deal of frustration, a learning curve involving the different types of foam and foam specs, layering combinations, and mattress “theory and design”, many hours of local testing on different designs and layering combinations to gain the personal experience you will need to help you “translate” foam specs into something that is meaningful for you, research into cover materials that may be suitable for your mattress, and can involve mistakes and the need to return layers that will in many cases offset any cost benefits involved in purchasing the layers separately. In most cases you would be much better off working directly with a manufacturer who offers the choices that you need, good value (sometimes better than purchasing separate layers), good exchange or return options, and perhaps most importantly the specific knowledge and experience that can help you make the best possible choices based on their experience with hundreds or thousands of customers. You can read more about this in post #15 here and more about some of the different specs that can affect the feel and performance of a mattress in post #2here.
To sum up … being your own mattress designer can be a fun and rewarding experience but I would approach it with realistic expectations of the challenges, risks, and potential costs involved. If the only motivation is to save money then it can also be disappointing as soon as you make your first “mistake” and can involve more of a learning curve and personal time and involvement than most people realize.