I have a 12g edge and a spec v. Either one is fine for a betta. I've had multiple bettas in my edge through the years (not at the same time obviously) and they've all found the air opening without issue (they have to battle the current of the filter, but they manage). If your betta is dumb, people have had success lowering the water level and then gradually raising it until they figure out the air opening. The edge is annoying to clean (takes almost as much time as cleaning my 50 gallon), but I still like mine. You may need to put a piece of sponge in the spec v filter outflow if the current bothers your betta.