Roon provides the metadata for you, in case you haven't done a great job tagging all those files. It also integrates Tidal and Qobuz (if you have subscriptions) so that they seem like part of your own collection. It uses its own network protocol, which has the advantage of presenting the identical GUI whether you're running it on a local computer or streaming with a tablet controller to a remote renderer.
JRiver is more customizable than Roon, cheaper, and has less of a hardware demand. It uses its own GUI when running locally, and it's better IMO in letting you edit the metadata (tags) in your own files. When streaming over the home network, you use a DLNA client on the tablet, so the GUI will be different.
I decided to stick with JRiver after trying Roon, because I had my files well tagged and didn't need Roon to do it for me. Also, my NAS isn't powerful enough to run Roon, but it is powerful enough to run the simple UPnP server that one can use without Roon. So I can access the server from any of the 3 or 4 systems in my house (and my phone) without needing another computer running 24/7 as a Roon server.
I hope I hit the right technical level with that, and that it helps.