Hi. I've added a 1  TB SSD (late model, WD-blue)...  and it works well. I've seen youtube video about replacing HDD with a SSD, but haven't tried it myself.

an aside, I initially tried adding an older version of SSD (something I've owned for several years) and while it was recognized by the system a problem did arise wherein the  Aurora R10 wouldn't "restart"-- would shut down, but not restart. This disappeared when replacing the older SSD with a newer (late model) SSD.

Thank you, that's what I was confused about. I thought that a 2.5" hard drive explicitly referred to an HDD, and I was confused as to why I couldn't just use a 2.5" SSD.

You can install a 2.5" SSD.  

If you're having problems with the SSD you can try reformatting it GPT / NTFS and in the process removing old partitions, especially old boot partitions if it was previously had an OS installed.