Yep thats how I do mine. At first it was a little tricky. But I've done the process a few times now and it has gotten easier.DIY dividers take 1
DIY dividers take 2
If the dividers aren't tall enough to reach from bottom to top- just cut another the length needed.
4-5 bettas divided I would say, as it gives them enough room to be comfortable in. 5 bettas would be 4 gallons, minus a few inches off the top (to prevent jumpers) and a couple inches from substrate.. so it would equal to roughly 3-3.5 gallons each, a good number.
BTW I just UNdivided my 20G and turned it into a sorority tank. But I still have glue stripes down the sides - does anyone know how to safely remove glue from inside a tank? I thought about using goo-gone or something but not sure if it would make the tank unsafe somehow.
I plan on doing this once I move in June and re-set up the tank in the new place.