Yes, that's an excellent deal. I paid about $30 for mine.
The 5300 runs well in the Mini, but needs a third antenna to operate properly with Wireless N. Get the drivers from Intel's web site.
Supposedly, the 5300 will allow you to use the new "MyWiFi" feature that turns your laptop into a wireless access point. It is not clear to me if that simply requires the newer version of the Intel ProSet software or something else. As I am running Windows 7, I'm using the OS drivers for the card and have not felt the need to install ProSet.