Hi pix530,
Having two twin XL mattresses can be an advantage for couples that have a different firmness preference, for couples that sleep on an adjustable bed and wish to use each side independently, and it can help with motion isolation as well (although that’s not normally an issue with a latex mattress).
Having said that … it’s really a personal preference although unless there is a specific reason to choose otherwise … most people tend to prefer a king size vs two twin XL’s so that there is less possibility of feeling any gap or soft spot in the middle of the mattress … especially if you tend to use the middle of the mattress. There is more about the pros and cons of split king mattresses in post #8 here and in this topic.
While a king size latex mattress is certainly heavy and would be more difficult to transport and deliver … I don’t see any reason why they couldn’t deliver it and it’s certainly not an issue for other companies that make a similar mattress.
Phoenix