I got the shield too, it's amazing. Upgraded from an old Chromecast and it's night and day, didn't realize how slow the Chromecast was, even on Ethernet.
I was seeing the Moana promo with my Roku streaming stick on a Samsung TV. Didn't look like an ad exactly tho, just a nice ocean background behind the menu.
personally I prefer android streaming boxes, because you can install custom versions of android tv on them, so if the official release from google is bad, you can just go to the community version
lineageOS, but you have to have a supported device, and I'm not seeing that device on there. Plus fire tv's are pretty locked down. I would suggest walmarts onn 4k box or an nvidia shield