It found no problems, so it run it out, and then make a decision. (It seems to me like a lot of money for what I call "paranoia-ware".) Have you checked its reviews on MacUpdate...always worth a look?
The demo runs for 30 days or 15 launches, whichever is longer.
Note: I didn't research whether the demo is restricted functionality.
(If you bought AppleCare with your iMac, the TechTool Deluxe disc that came with it can run a surface scan.)
