Roku3 player has some limitations and some benefits. Besides being a streaming box it works pretty easily with little hassle. Hundreds of free channels but maybe 5 of them are only worth keeping. I bought it for my wife who likes Asian Dramas on CrunchyRoll and DramaFever. It can stream from YouTube but at the time it had to jump through a few hoops as Google is strict on who can use YouTube. It can be slow compared to other services but it's cheap.
I would have gotten a Chromecast if not for Plex. If I must watch YouTube then there are my gaming consoles, roku, laptop, phone, ipads, etc. With Plex I have setup my media server and can watch any of my movies from any internet source; browser or smartphone, tablet, etc. Streams ripped blurays at good quality and was cheaper than Chromecast. I can share my library so anyone else can watch my movies too. Pretty cool to put all the kids movies and shows onto a media server where they can watch on their ipads from their grandparents place. Saves bandwidth too.