It will work, but as TeddyR stated, Commercial Detection takes a while. I ran with one for a month and was happy with it as a DVR. I was not using it for transcoding with Plex, but I did use it as my plex server as well. Additionally I paired it with HDHomeRun Extends so all my content was transcoded at time of recording…
I did end up moving to a PR4100 more because I could consolidate a lot of storage under it, and remove the need to have both a NAS and MacMini in the picture. (And I do now love the ability to watch remotely (which uses the transcoding ability of the NAS))