OK, so I tried it on an iPhone and it is super smooth and the text typing renders at a reasonable speed. For some reason on Windows in either Chrome or Firefox the whole thing runs at like 5 fps and is super bugged. This is probably the reason so many people gave up on it. You can't just click through the text, you have to wait for it to slowwwwly type out each page which for the first one takes minimum 30 seconds, even while clicking and pressing enter to speed up the text.
That animation is credited to someone else.