I bought the Noctua Case fan as a replacement for the standard fan in my Synology NAS DS114. I immediately replaced when installing the screws from the old fan through the rubber plug supplied and the Noctua fan runs as opposed to the standard fan silently. You only hear it when you go to the ear to the NAS and as we hear only the air flow. The cooling of the NAS is just as I expected it to me.
I would buy the fan at any time and I think it is definitely worth its price. A strong buy recommendation!