Unfortunately, this has been my experience with all SD cards I've tried. Even ones sold as high-performance are just annoyingly slow to use as a root FS.
They also seem to be extremely unreliable when used with even a modest write load, often failing within a year.
As a root FS, agreed. As an expansion, I have had really good luck with the 256GB microSD card in a low-profile SD adapter on my MBP. When I'm doing screencasts or whatever, I happily dump my recordings out to it and, as silly as it is, it's one of my favorite pieces of tech right now.
