Yes, it seems like they've ironed out the supply issues. DD was moved from K math and lanuguage arts to 1st grade, and the courses showed up on the computer almost immediately and the supplies were here within a week or so.
As far as not being able to use anything other than what they supply - well, I haven't found that to be true. Our "teacher" has recommended other resources to us, and as long as your kids meet the objectives of the lessons, they don't really care how they get there. Because of their charter, though, the only things that can be turned in as work samples have to come from the k12 curriculum. So if you've found a different way to teach your child a certain subject, you just need to have them do one worksheet or something. I also don't find it to be workbook heavy - there are workbooks included for some subjects (math in the lower grades, composition, handwriting, and grammar) but nothing that is absolutely necessary to use. There are manipluatives included for math, and if you child learns better that way, there are extensive instructions on how to use them.
I want to say that some state seem to have a harder time letting kids move at their own pace than others. Depending upon their funding, some states only allow one course to be ordered ber subject per student, per year. That isn't a problem in California - as I mentioned, DD has already moved into a second course for math and LA, and DS was "skipped" a full grade based on test results and is now moving another year ahead in math, and probably will be in history within the next month or so.
I have heard not so good things about their high school program, so that's something we'll have to evaluate if we're still with k12 when that time comes. My oldest is only 7, but I suspect by September he will be in all 5th grade classes, and probably moving into 6th grade, so that isn't as far away for us as it might sound.
You do have to participate in standardized testing, though, which is one of the only negatives for us. However, it seems more like a PITA than an affront to my philosophy, since I don't plan on paying much attention to the test results.
I know there's a lot of debate over whether homeschooling charters are "really" homeschooling, and I've decided that, frankly, I don't care what other people think about it. I consider our family to be a homeschooling family, regardless of our affiliation with a school.