We have three Roku boxes in the house. They're the quickest and easiest way to get smarts in a TV. Plug them in and they work.
Started with Roku3 so we could stream Netflix, then a Roku1 to smartify an old projector to watch movies outside on the garage. Just upgraded a couple months ago to a Roku Stick ($45 USD), and honestly it does everything the Roku1 it replaced did, just a little bit faster. And that's about it. I loaded Plex on a machine and serve up a hundred or more movies for watching around the house. I specifically didn't go all the way up-range since they all do basically the same thing.
I am waiting for some of the usual cable channel providers to de-couple themselves from cable and allow direct subscriptions. Roku may be in the best place with their content-agnostic strategy, any provider could come up with their own app and you subscribe directly (many offer streaming apps and for now you authenticate using your cable TV account, which is really strange.) PBS has an app but it could be better, and as you mention the Roku is blind to it. The overall user experience becomes handicapped by the quality and eccentricities of the app itself (Netflix's app is both good and frustrating at the same time). The Roku search function does well to find a certain show across all of the online libraries. In general it works but the seems to be nothing breathtaking about it. Casting is convenient but my Android phones don't seem to support it.
You may not have experienced the oddities of the Roku app and how it struggles for control with the included remote. There's just something about how it is a dumb remote rather than an extension of the interface that is baffling to me. In my experience Tivo has a much better Android-app remote where it acts as a smart extension of the controls.