We love VfCR here. Both my 7th grader and 5th grader can work on it independently. The first day I have them write that week's words on note cards, then they do the excercises for the rest of the week. Every other week there is a review or test. We spend 20. minutes at the very most on each lesson.
Don't get the teacher's manual. Like another poster said, the answer key is cheap and perfectly sufficient. Also I think you could probably do two books a year. We only do vocab for half a year. My boys started their book after Christmas and they are almost finished.