Hi TemporaryCatatonic,
There is more information about the 12 in 1 customizable in the earlier posts in this topic that will give you a much better sense of how it compares to other mattresses and a forum search on “12 in 1 customizable” (you can just lick the link) will bring up more information and feedback about it as well.
Comparing the 12 in 1 customizable to the Ultimate Dreams Eurotop would be very much of an apples to oranges comparison because the Eurotop uses Talalay latex in the comfort layer which has a different feel than polyfoam and is a more durable material as well. There is more about the pros and cons of latex in this article.
Polyfoam is the material that is used in most sofas and upholstered chairs so most people are familiar with how it feels in general terms although it comes in a wide range of firmness choices and a sofa would tend to be in a firmer range than the comfort layers of most mattresses because your weight is more concentrated when you are sitting than when you are lying down so firmer materials won’t compress as much to prevent you from bottoming out on the sofa.
The Eurotop allows you to customize the firmness of the latex comfort layer before a purchase and you can also exchange the latex for a firmer or softer version if you need to after a purchase for a reasonable cost (see here).
The 12 in 1 customizable has 12 different configurations that are possible by rearranging the layers and using the firmer or softer side of the cover so you can customize the support/alignment and/or comfort/pressure relief of the mattress after a purchase by using different combinations of the layers without having to exchange a layer.
There is also more in post #4 here about how the 12 in 1 customizable compares to Tuft & Needle and there is more about the Casper mattresses in post #2 here and in post #3 here and a forum search on Tuft Needle or on Casper (you can just click both links) will also bring up more information and feedback about both of them as well.
There is more about the most important parts of the “value” of a mattress purchase in post #13 here. The choice of materials in a mattress is really a preference and budget choice (latex is a more costly and higher performance material than polyfoam) and the best way to know which one you would tend to prefer to sleep on or how you feel about Talalay latex comfort layers would be based on your own personal testing (describing how something “feels” is much like describing how something tastes to someone that hasn’t experienced a particular taste before and can be fairly subjective) and on more detailed conversations on the phone with each of the options you are considering so you can make the “final choice” that is the best match for you in terms of PPP, cost, the options you have available before and after a purchase to customize, exchange, or return the mattress or individual layers, and on all the other parts of your personal value equation that are most important to you.
The good news is that there are no “bad” choices or any obvious weak links in terms of the quality of the materials in any of the options you are considering.
Phoenix