I have downloaded Sheldon's PLL as well as the samples of Serl's PLL and compared the two. Also compared them to Mary Hyde's books (on which EFTTC is based). I think they are all quite similar and all seem equally good (to me), although free is always better. You could also create your own LA-grammar worksheets using pictures, stories and poems that you and your child read together. What you have to aim to cover is punctuation, capitalization, parts of speech, picture study, comprehension and composition. These books just make it easier by compiling good prose extracts, poems and pictures into one book.