It is encouraging news that you haven’t had to reboot the Shield, however it is seemingly off-set by problems for you with attached USB drives and utilizing Shield for other client activities. I haven’t used the Shield for “other” client purposes, i.e., Netflix/Amazon, so I cannot contribute any data experience. We use ATV4s as our clients. We were contemplating using our only Shield (non-pro) in our MBR in order to utilize Kodi (for complete auto comskip playback)…but MrMC (on tvOS) has now proven to be very capable for both non-Channels/Channels recordings with the newly added .edl file function on Channels and also utilizing a .txt/.edl file comskip production script for our older non-Channels recordings.
OP, per posting, appears only wants to use Shield as a Channels server…so the Shield may indeed be capable for that specific required use. Possibly @tmm1 can add his setup/experience with Shield. Also, @timstephens24 has experimented with Shield as a Channels server, hence his input would be worthwhile.
I originally purchased the Shield (2 years ago) as an Android playback device for DRM (based on SD’s projections). Ever since, as SD Android DRM was a complete bust, I’ve been trying to find a niche use for the Shield…to no avail. Especially now with just released Channel’s improved transcoding for my Qnap…I see no added value vs ATV4. May be able to utilize in the future, but for now it is an “excess” device in our household. 
