The HP Gen7 N54L is just below the borderline for what you need for 1080p transcoding. You might get away with a lower bitrate file or certain scenario but in the main it's going to struggle at transcoding 1080p. If you're not transcoding (i.e. m4p to iOS, or using Synology/QNAP apps) then you're not going to be too bothered about this. The QNAP TS-451 is based on the Intel Celeron J1800 @ 2.41Ghz, so it is not going to be able to transcode 1080p video (Plex forums link).
That said I think I get why Deuse has bought a NAS. The lack of maintenance, regular updates, easy to install apps and featured mobile apps (and I guess fixing subtitles) make it a compelling purchase if you don't need the horsepower for something like Plex.
I deliberated with this question for a long time and only recently replaced my old Synology with a HP Gen8 MicroServer running Ubuntu Server simply because I wanted to get away from using a NAS and use Plex heavily. But as mentioned in some scenarios the NAS wins.
Who the hell transcodes these days?
All my films that was on my N54L was in 1080p. Every device I have(phone\tablet\TV) is 1080p. And all worked great.
If a person is behind the times with their hard ware then yes, but who is these days?
Loving my Qnap