While the original recipe calls for buckwheat flour, you can certainly use other gluten-free flours such as almond flour or coconut flour. Each of these alternatives will impart a slightly different flavor and texture to the muffins. You can also substitute buckwheat flour for all purpose GF flour at 1:1 ratio. Almond flour banana muffins, for instance, will give a nuttier taste and a denser texture, while coconut flour, which is highly absorbent, will require you to adjust the amount of liquid in the recipe to avoid dry muffins. When using coconut flour, you typically need less flour than the recipe calls for with other types of flour. Just keep in mind that different flours have different properties, so the end result might vary slightly in texture and flavor from the original recipe that uses buckwheat flour. Experimenting with different flours can be a fun way to find your preferred version of these muffins!