I have an older version of this, the WD TV Live which I have mixed feelings about.
My box will play just about any format, but getting to play anything can be a bit of a chore because there is some serious lag in the UI. My wife who is less tech inclined doesn’t like to use it if she can avoid it because it is soooo slow. From what I can see on the mothership reviews, this wasn’t fixed in this version and probably won’t be because they have had this issue since the original WD TV which I also owned.
Also, from reading the amazon reviews, this unit discarded the Netflix support (which in my experience is only so-so on the WD TV Live anyways) which may or may not be a dealbreaker since so many devices play Netflix these days, but something to keep in mind.
My suggestion would be that if you are mostly concerned with playing local/network content and are tech inclined (or at least willing to put up with a bad UI) this is the way to go. If you want something that’s simple to use and is focused on streaming from the cloud, go with Roku.