I think if you're using it for a specialized application with eGPU support, game development, or gaming in Windows via bootcamp it's a passable solution (albeit with lower performance than a native card).

On the for something like web development, it's finicky - Chrome won't pick up on the external GPU unless you have an output directly from the Mac Mini to the graphics card along with separate output from your Mac Mini to your external monitor (which means a lot of plugging and unplugging cables whenever I boot up the machine).

If I could afford a Mac Pro or had space for an iMac, or if Apple actually made the xMac I'd buy those in a heartbeat.