My kids use it. For my older kid, who is finishing 5th grade math, she's mostly using it as a video game, and she's not working beyond her current instructional level. She did learn a lot from many of the videos last summer when we were patching a few holes her subject acceleration were going to produce. She wasn't able to internalize the methods from the Explain tabs in ALEKS, but the videos working the examples did a lot.
For my younger who will start kindergarten next year, we're finding it's great. Lots of problems, lots of encouragement, and decent video explanation of concepts he's already familiar with. He's unable to apply the video explanation from unfamiliar concepts (most recently it was long division). It's a decent compliment, then, to working directly with me, as we'll talk about it, he'll go back to the video, and then be able to do the problems.
Looking forward to the higher topics, however, most of the problem types are presented as multiple choice. At this point I would find it unacceptable as a learning tool because I have a family of extraordinarily good guessers.
Both kids have loved watching a lot of the other videos, and they're slowly working their way through all the cosmology and astrophysics videos.
