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Amazon is now automatically playing fullscreen video ads on Fire TV
(9to5google.com)
This is a most excellent place for technology news and articles.
Essentially yes, the Chromecast ultra is basically a more powerful Chromecast 2 that supports 4K (maybe other differences too but idk). I've stuck with the ultra because the next upgrade is one of the Chromecast "with Google TV", which while is nice that you can install / side load apps like SmartTubeNext it also means you get a dedicated remote (I hate having more remotes) and it also has a launcher, which I think is more likely to get ads added to it (not sure if it already does by default or not) compared to the older CC2 / CCUltra which just has a "backdrop" photo slideshow and no launcher UI.