While you might think it is very noticeable I have never had a customer want to switch to a one piece king after trying a split king (two twin xls).
Maybe once a year we have customers who buy an adjustable as a one piece king in order to avoid having that gap but my customers experience says there is no need to do so and pass up the ability for each user to control their own side of the bed.
If you want to reduce the noticeability of the transition we do have cool gel memory foam and latex mattress models that are squared, almost right angled, on the edges (see photo)
Many conventional mattresses waterfall (curved transitions (see photo)from top to side) that creates a small valley in the centre of a split king or split queen adjustable.
And if you’re worried about the two beds sliding apart more than the transition we do have a number of ways of preventing that from happening on delivery day.
Please drop by our Mississauga adjustable bed showroom and we had to show in person.