We've reached the two-week mark since enrolling my daughter in Time4Writing's 8-week "Extreme Paragraphs" course at the elementary level. She's at the last assignment of Week 5, which is well ahead of schedule, but the course went from easy, to challenging, just about now, and so I expect that her pace will slow as the difficulty increases. I think it benefits our homeschooling in that it jogs my memory about how to break down the teaching of writing, making me a better teacher even as it gives her a set of challenges from an external source.
So far, I can see benefits, and also some problems, with the mechanization of learning in this manner. Outsourcing to a private tutor is not an option for many families, but in any case, getting an 8-week course organized, graded, and run by someone else for $99 is a hard deal to beat. However, in approach and content, some of the sacrifices which are necessary in the name of automation, make this system compare very poorly to real one-on-one personal feedback, even the kind I recall from a teacher responsible for the whole class, in school. The teacher does respond promptly to any questions or concerns, though.
I'm not ready to make a full review, but am looking forward to seeing what we take away from this experience, ultimately.