QNAP has removed Roon app from their appstore temporarily because of security breach. Check out this thread for more info: QNAP security advisory for Roon Server - #6 by Miracle1980
I’m sure fixed version will return to QNAP appstore any day now.
And yes, Roon core runs smoothly on this NAS, no worries on that. Processor has plenty enough power. I recommend to add extra 4gb of RAM though, it helps a lot.