Hi zexpress,
I think that many people would notice the difference between an innerspring support core and a polyfoam support core although it’s true that the upper layers contribute more to the feel of a mattress than the deeper layers and both of these would have a more resilient feel than their other mattresses.
With the very limited description on their website it would be impossible to know whether their mattress approximates any of the Tempur-Flex mattresses but more importantly it isn’t possible to make any meaningful comments about the quality and durability of the materials inside it.
There are a number of other options for some of the “simplified choice” mattresses in post #3 here that are completely transparent about their materials so you can make some meaningful assessments about the quality and durability of the materials and the mattress as a whole.
There is always a significant risk involved in buying any mattress where you don’t know the quality and durability of the materials inside it and can’t identify any “weak links” in the mattress (see the foam quality/density guidelines here) because once the trial period is over there would be no recourse if the materials start to soften or break down prematurely and you lose the comfort and support that was the reason you purchased the mattress in the first place because warranties only cover specified defects in a mattress and not the gradual (or in some cases more rapid) loss of comfort and support that is the main reason that a mattress will need to be replaced (see post #174 here).
I would avoid any mattress where you don’t know the type, quality/density, and durability of the materials inside it.
Phoenix