[Fnoord]

My main complaint is that subtitles don't work with it (on Netflix, at least).

You don't have to use it. For me, it works when I'm trying to dual task on a single monitor. For example, I use it regularly on my smartphone (with a native video player).

As for the example you mentioned: the issue is autoplay. Netflix just rolled out an update when they allow you to disable that non-feature.

[conradfr]

Another thing with Netflix is that they somehow reload the page between episodes so you have to go back to the page and re-enable the PIP.

Youtube does not.