As I recall each of her log cabin rulers has measurements for two different sizes. I have not bought the rulers, though I did take her Craftsy class to learn the method she uses for log cabins. She provided paper copies of the rulers in the class materials and I used those when making log cabins using her method. My take away was that her method of making log cabin blocks is useful if you are making a quilt from either fat quarters or yardage-- if so, then you will save fabric and time because you precut everything before assembling your blocks.
However, if you are making scrappy log cabin blocks from your scrap stash her method may or may not be helpful. I did find that when doing it her way my log cabin blocks were less likely to get wonky than if I made them my usual way which is start with a square, find a strip, sew, trim, find next strip, sew, trim etc. Using her method your strips are already cut to the exact size (width and length) needed, so it becomes immediately obvious if your block is going astray. But you would not be able to cut as efficiently as you would if using fat quarters or yardage.
Hope that helps.
Rob