ROKU and Amazon fire stickers are the top sellers and billions hours are streamed on them. Upcoming Disney streaming only supports ROKU, not Amazon.
Reading some research paper will help you understand. Again, it looks expensive now but the mega trend is on ROKU's side.
P.S.
Steve Jobs tried to nail the TV business but did not live long enough to succeed. Apple TV is a gated garden. Google has chromecast but its share is shrinking. ROKU is neutral to all streaming service providers, and managed to gain the most market share so far. ROKU sells tools in the streaming TV gold rush, and take a good cut of the pie - that's how I view it.
If one company comes up a killer solution for streaming TV, ROKU will become worthless. But no giant is doing anything close. Comcast's free stick is good attempt but would impact ROKU in a moderate way.
Tradingthe stock is a totally different business. I'm not recommending buying it here either. Buying low and sell high is always the right way to go.