The only problem I had with this article is when he said, "Here we sell Betta aquariums with clear dividers that are meant to house two or more Bettas in clear view of each other. This is supposed to enhance their appearance, because the poor things puff up their fins, thinking their territory is threatened. What few people realize is that this practice is very stressful for the Bettas. Although the fish are not damaged externally, and what I mean by this is that they don’t tear each other up, internally they experience the same stress. We all know what stress does to our bodies. Well, it has the same effect on Bettas. How would you like to live every moment of the day continually angry?"
I have clear dividers for all of my tanks and at first they puff up and flare, but they eventually get used to it. I also have plants up against the dividers. Two of my fish that I've had together for over a year now actually get depressed when they aren't together. I personally think that they enjoy the company and I haven't once seen one of my bettas with a stress stripe over this; they sometimes get them when I do water changes.