Hi Christine,
It would really depend on the person and their thoughts about the importance of organic farming methods. Organic Dunlop isn’t really any different from 100% natural Dunlop that doesn’t have the certification in terms of feel, performance, durability, or safety so people who choose organic Dunlop latex would normally do so for personal reasons. There is more about organic latex in post #6 here.
Any mattress that is made two sided will benefit from flipping but of course only two sided mattresses can be flipped so one sided latex mattresses don’t need to be flipped (and can’t be flipped). Latex is a very durable material and one sided latex mattresses will last for a very long time but even a very durable material such as latex will last longer in a two sided version. There are also tradeoffs in a two sided design though and limitations in how a two sided mattress can be layered. There is more about the pros and cons of a two sided mattress in post #3 here and the posts it links to.
Latex in general is the most durable of all the foam materials (polyfoam, memory foam, latex foam) although all foam types have more or less durable versions. There is more about the factors that can affect durability and the useful life of a mattress relative to each person in post #4 here.
I don’t know which Tempurpedic mattress your friends are sleeping on but I would also keep in mind that their mattress would probably last much longer for most people (if the mattress was appropriate for their body type and sleeping positions) than it seems to have lasted for them.
Phoenix