With flex-head options, only the top portions of the bed have independent range of motion. The foot of the bed is still attached on both sides. With split options, both the head and foot of the bed can move independently. Either option makes a lot of sense for couples who want to pick individual firmness levels and the angle at which they sleep or relax. In the spirit of understanding the full scope of offerings for couples (and having never tested a flex-head option before), I ended up going for the flex-head king. I don’t think I would do it again, as I found I preferred the flex-head more in my waking hours than for sleeping. I would use my side to sit up and read while my husband slept. However, if I wanted my feet up for zero-gravity mode and he wanted everything level, we had to be on the same page, since the bottom of the bed was still connected. Having the split only at the top of the bed took some getting …