We are trying to use our Roku on an iPhone hotspot. The issue I have is that there is a 15 gig cap on our service. There needs to be an option on Roku to limit the bandwidth so we don't hit the cap in a matter of a few days. I did find the unsupported option of 5 home/3 rewinds/2 forwards but it always goes back to Automatic. Since we are using the iPhone there is no router to configure. Roku needs to address this situation.
You can reduce bandwidth usage somewhat by limiting the pixel resolution the Roku sends to your TV. System/Display type -- set this to 720p (or lower, if available on your Roku model) instead of the default Auto setting.
Edited to add:
Be sure you get in the habit of returning your Roku to its home screen when done viewing to prevent it from continuing to stream and eating up unwatched bandwidth.
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T