Oh, that looks awfully familiar! You found my setup!
Thats actually a 10 gl tank. In the inserts you see at the bottom of the pictures, are the males (some make very nice bubble nests there), and in the rest of the tank are the females swimming freely. The insert holds up to 5 bettas, and currently I have 3 10gl tanks set up like that, with around 8 bettas in each tank.
I found that way of setup very practical. The males grow and look happier because they enjoy filtration, not a little container with no filter. They have the looks of a natural tank with plants and rocks, and the females develop eggs better since they are in constant companionship with males. Thats all run by a spongefilter in each tank, and weekly 15% water changes, with added salt in the water. Bettas like that....
Glad you enjoy it!