Easy Grammar is better for a student who is working or must work independently, while Voyages would be better for a student who can work closely with his mother/teacher. The doctrine is clearer in Voyages, but the repetition is helpful in Easy Grammar. The editing books are to help the student edit, which is not the same thing as write, but is the skill tested on a standardized test. Some practice in this skill will help students do well on the standardized tests.  Either of these texts is good for editing.