The custom player experience isn't good. Tapping the progress bar to go to a specific time doesn't work reliably unless in full screen. Sweeping on the bar to reach a certain second isn't reliable: it's hard to hold it because the click box that triggers that bar hold is very thin compared to the bar of other players, and sometimes doesn't move the video to the selected time unless I pause and resume the video.
If the underlying video fails to load (eg non existent video) the custom player just shows a black screen, so you don't know whether it's loading or won't play.