I am one of the developers, and at the moment I wouldn't use it for critical stuff. We would like it to be good (not just functional) and that takes time. We are not in "1.0" stage yet, and we make backward incompatible changes from time to time. Specifically, if the proposal for tables is accepted, the package will change a lot (and it will be awesome). The CBLAS package should work well, and I believe all of the goblas functions that are there have good tests. In my opinion, Mat64 needs a lot of work before it is a "premiere" package (a bunch is missing and a bunch is slow). That said, I use it in my work and many parts of it are good. We are interested in making it better, but it's entirely volunteer and it all takes time. It would be great to have people providing code/documentation/bug reports, so I encourage you to use it in non-critical stuff.