Yes, it has worked perfectly, always on, 24/7. My only complaint is the noise.
I use a set of four 8TB Western Digital HDDs (Pro/Red label, 7200 RPM), two for data and two for back up of the other two. This has worked well for me. I’m not running out of space yet, capacity is currently 70% full; but buying an entire “complete seasons” TV show on BD would probably push me to the limit.
I have been seriously considering the DS920+; in fact, I bought it on Amazon recently, then I second-guessed myself and canceled my order (so much money!). When I do upgrade, I’ll want to replace my 8TB HDDs with 10TB at least, if not 12TB; I’m watching those prices too.