But the implementation is shitty and it depends on the game and the devs on how "4K" the title is. Some games have no pro tier version, and some have like 1440p30. The free tier is 1080p60ish and you pay for the games you want.
Input latency is really a non-issue. I don't think there's more to it. It's just not something you have to think about — until you do, but it's been pretty rare for me.
Also you can play it on every desktop platform via Chrome, and via Safari on iPads and iPhones. Works on Android too.
And of course Google is going to kill it probably soon :)