I have used it in the past, and it did work pretty well, once everything was setup, it could even transcode if you wanted.
I never used it for viewing though, only recording, and transcoding, and then view it from another machine.
Linux is pretty nice for a NAS.
Haven't tried it in 3+ years though, I am just using NPVR right now, and that meets my needs.
I'm currently running a Lubuntu setup with a MythTV backend installed, Kodi running as a frontend on that computer and Raspberry Pi3 running a Kodi frontend upstairs, HDHomeRun Connect (I think that's the specific model, no encrypted channels needed). I played with several flavors of*buntu, and MythBuntu was by far the easiest to get up and running. You can install it on any *buntu system using Mythbuntu Control Centre, but it takes a lot of tweaking/frustration to get the MySQL setup working right. At least it did for me, being rather new to Linux and MySQL. MythBuntu made that a lot easier, but then it requires some tweaking to Kodi running seamlessly (I had sound and Harmony remote issues). With regards to the HDHomeRun, no issues whatsoever. That was the easiest part of the whole setup. I've not used the Myth frontend at all, so no comments there. Once the initial troubles are sorted (specifically the MySQL issue), setting up Myth using the guide on their main page was fairly straightforward, and Myth is really cool once you figure it out. I had no trouble with HDHomeRun or SchedulesDirect with Myth.
I run this system as a basic NAS for the house, with a RPi and Win7 system connecting to it via NFS and Samba respectively. If anything, MythBuntu is a bit easier for me as a Linux noob than some of the other more stripped *buntu flavors.