My experience was quite negative though. I tried to transcript the knife game song, but when it's picking up the speed, it skipped some words and I couldn't add them perfectly. Then I couldn't remove my errors because it can't edit more than 5 words at a time, and automatically select more. I fought with the UI for more than 10 minutes and when I tried to download the video to get the (best I could get) imperfect result of my hard work, contrary to what you said ^^ it requested my email so I couldn't download it.
The timing of the lighting of the words is almost OK, but there is a noticeable increase in viewing experience when the words light-up at exactly the right time.
It still needs some UI bug hunting to make it usable but it's on the right track.