I chose the K12 program for High School Biology. It was ok. I did not love it.
The pros: There is a teacher that your student must report to. My son had to log on, read his Kmail, read his assignments, take the quizes, take the tests, do some labs at home, write up reports, scan and submit them in an online drop box, discuss results on a discussion board with other students, and watch some class connections (video conference for the class). This is important in the progress of moving from mom as teacher to college.
The cons: My son did not love it. I don't think he caught the joy of learning. The material is presented in a boring way. I don't think he learned the material that well. He got an A first semester, and a B+ the second. He did learn just as much as my two older kids that went to traditional public school. So, I don't feel like we lost there. I just want more. After this year, he said he preferred the Plato Science program. I think we will choose that for Chemistry for next year.
So far I loved the middle school science program by Plato and Adaptive Curriculum.