I think the choice between Dunlop and Talalay is strictly a matter of personal preference and not a “better worse” comparison. I personally for example prefer the “feel” of Talalay but my daughter on the other hand prefers the feel of Dunlop (after testing both) and she recently purchased a mattress that is Dunlop from top to bottom. At least we both like latex
This article along with post #6 here compares the relative cost or value of each type of latex but in very approximate terms … organic Dunlop (100% natural dunlop that is certified organic) and 100% natural Talalay are in about the same cost range, blended Talalay and 100% natural Dunlop are in the next group down, and then blended Dunlop is generally the lowest cost version of latex (outside of latex that is mostly synthetic Dunlop such as “smart latex” used by Sealy or some … but not all … of the latex mattresses at Ikea). I think the best “value” for most people (but not all because preference and budget makes a difference) would be blended Talalay or 100% natural Dunlop.
In terms of your choices … it’s difficult to say because you are in a place where all of your choices are good ones and the parts of your personal “value equation” that are the most important to you will play just as big a role as the “commodity value” of the mattresses you are looking at. No matter which mattress you buy … at the end of its life you will remember more about how well you slept while you owned it than you will about how much you paid when it was new so its PPP (Pressure relief, Posture and alignment, and Personal preferences) is a significant part of the value of any mattress purchase.
If everything else was equal … then the “value” at Flexus is great but a smaller manufacturer can’t carry every possible combination that is available and if you don’t quite “fit” one of the combinations you tested then even if he could order a different ILD there would be some extrapolation involved about whether it would become your “ideal” construction. For example with 3" of 24 ILD Talalay over a firmer version of Dunlop it may be “just right” for you but I don’t know if he has firmer Dunlop on the floor or exactly what he has available.
At Electropedic … they have a slightly different construction and they also have the benefits of a two sided mattress. All Talalay isn’t’ any better or worse than all Dunlop or any other type of latex or combination … it’s just a matter of preference (and of course the “value” and cost of the different types of latex).
With Diamond … I would want to know the missing details of the layering so that I could make more meaningful quality and value comparisons and better identify any potential weak links in the mattress but I don’t believe they would be “poor quality” materials even though they may not have the same value or longer term performance or durability of an all latex mattress and they are different from the rest because they are a more complex combination of latex, polyfoam, memory foam, and pocket coils. This wouldn’t be in the same “value range” as all latex mattress (which is a more costly material than the others) but again its comfort and performance may mean that it’s worth it to you to pay a little extra or to take the chance that it won’t be as durable (or keep its comfort, support, and “feel” for as long) as as the all latex mattresses you are also considering.
So I can’t really tell you what to choose because all your choices are good (although I would be less comfortable with a blind purchase with missing information) and much better than what you would otherwise be considering from a major manufacturer or mass market retailer) but it’s more a matter of “how” to choose between them. For me this would be a step by step process of comparison, tradeoffs, and elimination based on a combination of the quality/value of the materials, how they perform and feel in your testing, and all the other benefits and options that are part of each design and the retailer or manufacturer you are buying from. Final tradeoffs are difficult when there are parts of each that you want to combine in a single purchase but that’s not usually possible so it becomes a matter of choosing which one is best for you based on the objective, subjective, and intangible factors of both the mattress and merchant that are most important to you.