It has only one issue: when playing the next video in a playlist for some reason causes the window to scroll down which leaves the top of the video hidden. This is not a minor issue and that's very unfortunate because this extension would be perfect otherwise.
EDIT 1: Reading back the review several users reported the same issue, some over a year ago.
EDIT 2: Workaround by commenting the scrollTo function in ythd.js and disabling auto-update.