Yes, I bought the Shield to use as both a PLEX server and client. It took a little time for me to discover that unlike a PC I couldn’t just attach an External HDD to one of the Shield’s USB ports and instantly setup the PLEX server.
I had to first format the HDD to Wipe the drive completely and merge the HDD with the Shield’s internal storage. The issue here is that once formatted on the Shield the External HDD will only work on the Shield (unless re-formatted for PC). This meant that I couldn’t remove the HDD from the shield, connect it to a PC and add media. That left me with an empty 4TB HDD while all of my media was still on my PC’s HDD.
After lots of Googling/YouTubing I discovered that I’d have to first mount my PC as Network Storage to the Shield and then transfer my Media across the Network directly to the Shield. It works great now but it definitely took some time to figure out the process. There is a lot of conflicting information on the internet and especially YouTube. Hopefully this helps you avoid the same pitfalls I encountered.