Hi jasonsmith,
You’re right that in the lower budget ranges that lower density foam would be more likely although I would still want to know the specifics rather than speculate. I would also doubt that most of their mattresses used actual HR polyfoam and it’s probably HD (HR is a specific grade of foam that uses a different chemical formula and is 2.5 lbs density or higher, has a compression modulus of 2.4 or higher, and has a resilience of 60% or more). Many foams that are listed as HR (High Resilience) are actually HD (meaning High Density although they are still good quality in most cases).
If lower density foam is also convoluted and there is more than “about an inch or so” in the comfort layers then it would be less durable than a solid layer and could certainly be the weak link of a mattress.
Sleep Essentials is certainly a good quality/value mattress and I also think highly of Lee (the owner) although I would take some of the information on their videos with a grain of salt because some of it is somewhat inaccurate or misleading. Mattresses that have individual component layers that can be exchanged are also a very flexible design and similar designs are quite popular because it gives you the chance to make comfort adjustments if necessary after a purchase and as you mentioned it can also allow you to change out the comfort layer if it softens faster than the other layers or if your needs and preferences change over time. They also are sold without a fire retardant (you need a prescription from a health professional to purchase it but this is normally a simple matter that they will help you with if necessary). They would be well worth a visit and you can see some comments about them in Clawdia’s posts in this thread and a forum search on sleep essentials or on perfectlatexmattress (you can just click these) will bring up more comments about them as well.
Phoenix