Hi robromo,
There are a few important parts of the mattress shopping tutorial that you may have missed (and I realize that there’s a lot of information there) so I’ll expand on a few of them here since they answer most of your questions.
The choice between memory foam and latex is a purely subjective preference and not a “better worse” choice. There is more in post #2 here about how they compare but the only way to know for certain which one you may prefer between a fast response and non temperature sensitive material (like latex) and a slow response and temperature sensitive material (like memory foam) is your own personal experience. It may be a good idea to test each type of material at local stores to see which one you tend to prefer.
The only way to choose a mattress is either based on your own personal testing and experience or if you can’t test a mattress in person then a more detailed conversation with a knowledgeable online retailer or manufacturer where you can provide them with more information about your body type and sleeping style along with the mattresses you have slept on in the past or tested and liked. Nobody else can feel what you feel or tell you what you may prefer based on “theory at a distance” (see mattress firmness/comfort levels in post #2 here)
The 12 in 1 uses 2 lb polyfoam which is a good quality durable material. There is more about the factors that can affect durability and the useful life of a mattress in post #2 here and posts #28 - #30 in this topic also had some questions that were very similar to yours which should be helpful.
The Tuft & Needle is a firm mattress that uses almost the same quality polyfoam as the 12 in 1 (about 1.8 - 2 lb), but since it can’t be customized it would be of most interest to those who prefer a firm mattress. It has a great return policy so it would be an all or nothing choice that either works or doesn’t with little risk.
The 12 in 1 customizable would be suitable for a much wider range of people because it has many configurations from soft to firm. While there is a return policy (if you order it from the Dreamfoam site) there is a modest cost involved. A component mattress also has the advantage of being able to replace just a single layer down the road if one layer has softened before the others (the comfort layers in a mattress will generally soften before the other layers) or if your needs or preferences change over time without having to replace the entire mattress. The short answer is that this is not a pocket knife example where something is sacrificed for the sake of convenience.
Both are good quality/value choices (and there are many mainstream mattresses that use much lower quality polyfoam in their comfort layers) but one is much more versatile and the other one is more dependent on its return policy to lower the risk of an online purchase.
I would also be very cautious about using mattress reviews as a way to choose a mattress since “comfort” is very subjective and what works well for one person may be completely unsuitable for someone else to sleep on (see post #13 here).
I hope this helps you make the final choice that is the best match for the parts of your personal value equation that are most important to you 
Phoenix