ProTube pulled from the App Store →
Unfortunate, but expected. Picture-in-Picture (PiP) mode and background audio are two of YouTube Red's most convenient features on mobile, so it's unsurprising to see YouTube snuff out any third party apps that do the same without the subscription.
What I'll miss most is ProTube's implementation of video playback speed. The new YouTube app (finally) includes it, but requires 3 taps to activate and has to be manually turned on every time a new video loads. Even worse is that the audio becomes unpleasantly tinny, similar to the way sped-up YouTube videos sound when watched in Safari versus Chrome on macOS. My guess is that it's an OS-level HTML5 video playback issue that Google will hopefully encourage Apple to fix.