They are lovely
I have a male and a female although they are in seperate tanks. To the pp lots of people say 3gals as a min. My personal preferance is 6 (29ltrs) it gives you enough space for a filter, mini heater and to plant it out. Bettas really like plants so it's nice for them to have them. My male loves his tank! My female loves hiding in the plants.

Back on topic, I really love the betta you have in your avatar