I wouldn't put a sorority into a divided tank, because that would probably be too much stress. But just two bettas, or a few depending in the size tank, will be fine. Some bettas get stressed in divided tanks, others seem to love them. Double up on dividers if you can, and make sure there are some plants to break their eyesight.
The only real downsides are it's easier for them to spread diseases, and it's easier for them to jump a divider and fight than to get from separate tanks. On the other hand, you can easily have a stable cycle and only need one of each piece of equipment.
10g divided; Claude VT & Marie VT | 5g; Gabriel DeT(?) | Mom's 2.5g; Hank DeT