We've tried a bit of homeschooling over the years, and there is an important difference between what looks good to parents and covers the required standards, etc.... vs. what actually engages our children and makes them satisfied with their educational experience.
We never tried K12, but I recommend that the kids be involved in selecting what tools to use, as they are the ones who have to use it every day.
It's designed to keep kids and parents busy for ~8 hours a day, because their customers are online charter schools, not homeschooling parents.
These online charters get paid based on attendance, so it's in their interest to have kids occupied all day every day.
Please, do not ever use K12. It's terrible.