We did K12 in a virtual school setting (public school), so here's my EXPERIENCE/OPINION, your mileage may vary. It was a public school. At home. There are attendance requirements and progress requirements and teacher phone calls and face to face requirements, etc. Understandably, some of this will vary by state, but please do remember it is a PUBLIC school and you are your child's "facilitator", they have a teacher. While this works fabulously for some people, it did not work for our family. For starters, I travelled. a LOT. and I took the kids with me. They have been to every state east of the Mississippi except for (ironically) Mississippi.

They have seen more of this country and its heritage through travel than most kids get in their whole lives. K12 had a problem with that. I was well within our times/days, but I was always getting calls or emails about attendance. Thanks, but no thanks.
My now 13-yo has selective mutism and asperger's. She's not a chatty kid. Her teacher would get upset because she would call and DD refused to talk to her. IEP or no IEP, it became an issue.
The curriculum, while excellent, is rigorous. Code of Hammurabi in the 2nd grade. Yeah, it took me until my sophomore year in college and I was an history major!

Some children revel in the challenge, mine were frustrated by it. In hindsight, I'm not sure it was the actual curriculum as much as it was the overwhelming amount of "stuff" they HAD to do (art and music were actual lessons in addition to what I already had them doing). I don't believe that all children, and most certainly not mine, are the most brilliant, darling, little geniuses, so I prefer they learn on their terms and how they learn best as opposed to more of the same programming from a traditional public school.
Children are naturally inquisitive and are wired to learn as long as grown ups don't burn it out of them. We unschooled for some time, using lapbooks and online resources frequently until this year when we've moved into Oak Meadow as DDs both seemed more stable and prepared for a curriculum again. In the meantime, 11yo can give Ace of Cakes a run for his money,can make a mean alfredo, and has already bookmarked a few culinary schools. She is also working on ways to help combat violence against seal pups and knows all about the various seal species, habitats, etc. These are not things that K12 or any rigid curriculum could have taught her.