It's a genuine crypto "currency" in the sense that it's stable. It's matched 1:1 to the dollar, and people use it to hold stable monetary value, which can be traded for other cryptocurrency on exchanges, in an otherwise volatile market. For example, lots of people put their money into Tether during the recent market crash in order to protect themselves from losses.

A cryptocurrency like Tether is extremely useful for the reasons mentioned above. However, Tether itself is under investigation for not having the funds that it says it does, and I would be cautious before pursuing any Tether investments at the moment. Besides, I think that they've closed new signups anyway, unfortunately.