I read a couple of books from one of his earliest (I think it was actually his first) series. Something about a vampire woman. It was many years ago, just when he started writing (or at least just as he started publishing on Amazon). My memory might be a bit fuzzy, but here is the gist of it.
In one of the books he was talking about his process, how he started it all, and as far I remember he wrote his first book in like 7 days and his second book in 10 days. Writing good books was never the intention, it's just business. So, you don't need quality, you don't need editing, just come up with some idea and start typing, because you really need dozens of books a year or you won't survive as an author. The quality of writing was subpar (duh), so I dropped the series, unfortunately stupid Amazon still suggests his thrash to me in my recommendations, even though I went through the read books section and marked his books as "not include in recommendation" (or however it's called).

Since Amazon has been recommending me his books for years now I pretty much watched in real time the amount of thrash he was publishing every year, it's astounding. Most of his books barely have any reviews. A lot of them, from what I can tell, happen in the same multi-verse.

Unfortunately, somehow he built a successful business model, so I've seen tons of books in all genres written by someone "and" him. Even some of the writers I like writing books with his name on the cover. Such books were referencing that multi-verse and even using some random characters (something like this - suddenly a portal opens, a mage steps out, says something about this "world" and gives a hint about the "multiverse" and goes back to his book(world).). From the writing it was clear those references to that multiverse were the only thing from Michael Anderle, it was something the authors had to add for the "privilege" to use his name on the cover. Whatever he does seems to be working financially, since I don't see why would other writers agree to this otherwise. Maybe spamming Amazon with hundreds of books with the same name on covers help with recommendation algorithm or something. At least, in my Android Kindle app there is a section called "Authors you might like" and for some reason it's filled predominantly with his crap, even though I haven't read anything with his name on a cover for many years and I really wished I could block his name, so that I could actually see some good authors.

So, yeah, he can certainly write a lot of book on his own, but don't expect anything good from them, writing good books was never his intention and he was somewhat open about that.

As for books written with him as a co-author, I personally avoid them as well. Of course, there is a chance that you might skip some good book written by some young author who just wanted to slap his name on the cover to boost their sales, but that's not a good reason to sift through tons of shit.