Hi DrRich,
Here’s what I “think” 
You have done some great research and testing and eliminated all the “worst” choices (I don’t think you even considered any “bad” choices)
Your body, some objective and subjective testing and the help of some very good local “experts” has told you which mattresses are the best “match” for you in terms of PPP (Pressure relief, Posture and alignment, and Personal preferences)
Your own criteria is the best way to decide whether any extra cost of one mattress vs another along with the benefits and options that come with dealing with each retailer or manufacturer makes one a closer match to your own personal value equation.
At this stage only you can know which is best for you and any “theory at a distance” would not be helpful. Once you have narrowed down your list to choices between “good and good” which you have (and there are no warning signs in any of your choices) … then its time for me to step out of the way and your own preferences and what is most important to you is the only way to make final decisions.
Some of the benefits of thicker layers or mattresses are in post #14 here. In most cases 8" to 9" is all most people “need”. It may not be what some people prefer however or in some cases the design of a mattress that they prefer or that can accommodate weight differences or other challenges may make a thicker mattress more desirable. Everything is a matter of your needs and preferences in combination with the design that makes your needs and preferences possible.
Each manufacturer can tell you better if the specific materials and layers they are using can work well on an adjustable bed but in this case the answer would be yes. My own mattress has 11" of latex and conforms to my adjustable very well. Some mattresses that have over about 12" of latex may not conform quite as well but they would still be OK as well in most cases.
I like both of these and think they are both good quality and value. The differences between them are a matter of preference and the importance to you of being able to access and change the layers in your mattress. I think that zippers can certainly add flexibility or “value” to a mattress design and allow for changing layers if one wears out faster of if your needs and preferences change in time but there is also value in a two sided mattress which can be flipped. once again it’s a matter of what is most important to each person and which features they “value” the most. When you are down to all good choices … I don’t tend to think in terms of better and worse any more but only in terms of differences in features, options, ad preferences which may have more or less value to each person.
I have no personal experience with them and I haven’t talked with FSF about them so I am really not the best person to ask this. I should probably be asking you since you have seen them
Based on the online description though they seem very nice and based on my knowledge of FSF I doubt they would carry anything that they didn’t believe had good quality and value. It seems similar to the St Dormeir (which I like) or one of the wool/cotton Natura mattress protectors (which I own). Personally I like this style of protector.
Phoenix