Foucault's distinctly french and distinctly intellectual. The two are definitely touching the same elephant, and if you like Foucault you'll probably find something in Illich, but Illich appeals to a less intellectual and more American (religious?) audience that would turned off by -- or simply never get past the first page of -- Foucault.

Religious fundamentalist homeschoolers will read Illich and get something out of it, but would probably not have the patience/reading comprehension level to engage with Foucault. Or, if they did, would burn it.

So, both have their place.

That said, I wish Foucault had provided a more thorough treatment of schooling, though. I think his reaction to schooling was something like "yeah that's so transparently a factory floor look-alike and so transparently training compliant factory workers that I'm not even sure it's worth saying much else".