We have had Sleep Number beds for 15 years. We bought one for the guest room that was solid clear across. A person can't change the firmness on just one side, but can change it overall. Our bed has two chambers. I didn't like the little ridge in the middle if we both had different numbers, i.e firm and/or soft, so I finally set them both sides the same number so there was no little ridge down the middle.
The plus is, they don't have to be turned over periodically as they won't develop a dip where you sleep. They are more sanitary, easy to vacuum occasionally. (once every 10 years, haha.) They are lightweight and easy to move to vacuum underneath, or move from place to place. You don't need someone to help you move it.
The minus side: After 15 years, the middle partition broke down, so now we have this huge dip right in the middle. We plan to replace it with the same Sleep Number mattress, but we won't get two different sides this time. We will get one queen size so the middle can't break down if I live 15 more years.