I have an edit that I think might be controversial, but I don't expect that anyone is watching this discussion page, so I'm going to go ahead and make it before waiting for feed back. But let me just explain so that there is some context.
I went through a process of trying to select a library and made the mistake of starting to use one (eigen) before I really understood it. Instead my decision was based on a superficial review of what I could find out there, and some word of mouth suggestions from other developers. While it's easy to find a list of reasons why someone *should* use a lib, it's less common for projects to publish a list of why now.
For me it turned out that the issues related to alignment, that come from aggressive optimization, are a trade off that is not appropriate for my project. However I would have liked to have figured that out before having started integrating it into my project.
So I'm trying to prevent that from happening to other developers.