I homeschool too and we've been using their math with grade levels as our full course for a couple of years now. I don't know why it would be considered just supplemental.

Awesome. Great to hear. Have you found each grade level quick to get through, or rather lengthy? Must need for parental support?

If the lessons are done on a regular basis (I do them daily) then I don't think they go longer than a school year. But it would be easy to do the breakdown by looking at the outline for the grade level you're interested in to see how many lessons there are total (the lessons have a star next to them). As for parental support, it depends on how well your child can grasp concepts from watching a video explanation (the teaching videos are all quite short -- about five minutes) or looking at the step-by-step hints. Both my boys appreciate me being next to them so they can talk through the problems and have me check their work before they hit "return" to submit the answer. But if you have a really independent worker then you shouldn't need to hang around. 

Great. Thank you.