So far so good! I use this primarily as a Plex server, and it does just that. I only have 2x 2TB WD Red drives installed setup as RAID 1.
The web interface that WD wants you to use is just OK, and I feel it lacking in many features that would make it so much easier to use and navigate through. Uploading from my Mac through this interface has not worked at all. I am not sure if is my browser settings or what, but I used 3 different browsers, and the same result - unable to pull files from my Mac. However, when accessing directly from my Mac Finder, I had no issues transferring files over WiFi. I chalk this up to a learning experience, and now that I've found this, it works well for me.
I haven't tested this with simultaneous streams of transcoding, but the server is very fast and responsive when accessed over my Shield TV, Pixel phones away from home and Amazon Fire TV 4K dongle.