I don’t have experience in self-publishing, but based on my single stunt with Manning, I have a strong feeling that EiA is much better book due to their involvement.
In particular, Manning provided great editors, reviewers, copywriters, and proofers, and all of these people caught many issues at different levels. With self publishing you either need to hire these people, or otherwise try to do the job yourself. Therefore it’s more likely that (all other things being equal), a self-published book will to some extent be of lesser quality. However, if you are able to find good editors and reviewers, that doesn’t have to be the case.
Another possible benefit is that a publisher might give the book a wider visibility. Also, I feel that some people are likely to buy a book from a respected publisher, than from a lesser known author, because a publisher maintains a certain quality standard.
As a downside, if you sign with the publisher, you might end up losing the ownership of the work. In other words, the script now belongs to the publisher, and if at some point you want to leave, they can carry on without you.
They also have a big influence on how the content has to look like. You still get a lot of freedom, but not 100% you’d have if you were self-publishing.
Another possible downside is tooling. If the internal toolchain of the publisher is bad (perhaps because of legacy reasons), then it becomes harder write the book and to update it later. Manning used to be notorious for that. It’s been more than a year since I worked with them, so maybe something has improved, although I have some doubts Also, when it comes to Manning - due to their toolchain, syntax highlighting was not possible at the time I was writing the book. So that’s another possible issue (depending on the publisher of course).
And of course, a publisher will take some cut of sales, possibly way more than 50%.
So there are pros/cons for both approaches. I’m personally very happy that I’ve done my first book for Manning. The product is much better owing to their involvement, and I’d recommend anyone to write the first book for some publisher. That being said, if I’m ever going to write another book, I’ll strongly consider self-publishing it. It will require more work, and some financial investment, but I feel the final product could be better, I would have a full creative control over it, and I’d end up owning the product completely.