This add-on is perfect, and works great 99.8% of the time. The other 0.2% is when Youtube is changing their coding and it can take several days for the add-on writer (dishita) to update his code to match.
THERE IS SO MUCH B.S. WRITTEN ABOUT THIS ADD-ON. THIS IS HOW IT WORKS:

FREE users - add it on and you can download medium mp4's and most 720 mp4's.

PAID users - You can download all 720's and any 1080's if they are there. It's these DL's that make use of his server, and he has to pay for that himself. That's why we donate.
ANYONE who is having trouble can email him directly and he responds quickly ALWAYS. Enjoy!