I doubt you'd get the Bettas to eat flakes, most either won't go near them, or will spit them out. Micropellets for tropicals/Bettas are the way to go, with some frozen blood worms of brine shrimp every now and then. I prefer bloodworms, because I think brine shrimp has more of a chance not being found and eaten. Actually, I drop my bloodworms in one at a time with tweezers to make sure that each one gets eaten. That's mainly because my Bettas don't have a filters, and I want to make sure the water is kept as clean as possible.