I am new to all thsi by a few months but I wishI realized this: If you are going to keep a lot of bettas, as long as they are healthy and have no communicable disease, it would have been cheaper and easier to have several in a large tanks. I have 6 bettas. The more tanks, the more filters and heaters and lights you need. If I just got larger tanks and made the cheap dividers, it would have been much cheaper as far as buying extras for tanks.
Oh and I got the 10 gallon during the $1/gallon Petco sale. It's my biggest yet cheapest tank.