The smaller the sqaure the better the blending of the colors and fabrics. many of these use the grid iron on interfacing. You can position all of the squares prior to sewing when you use the grid. It goes much much faster. But the interfacing adds stiffness and is typically used for wall hangings.
I suggest you get a bit of the grid interfacing and see if you like it. Note " the one with yellow lines is the iron on the one with blue lines is not iron on.