Tom, are you able to power on your TV using the Roku remote while it's plugged into the USB slot on your TV? All of my TV USB slots are powered off when the TV is . I have to plug my ROKU power into the wall to have the Roku power on the it's remote.
Chromecast capability is already integrated into the apps/services on my phone that I want to use. And there's quite a lot more stuff I can cast from my desktop browser to a Chromecast than to a Roku stick.