Is it legal to download videos from YouTube?
Here the overal situation is quite clear: You do not have to worry about being sued for downloading YouTube videos. In most countries it is legal to make a private copy of YouTube videos, however it is not permitted to share this copy with anyone else.
By downloading a video from YouTube, make a "Private Copy". These private copies are legally allowed when downloaded from a legal source. YouTube is such a legal source because every user voluntarily uploads their videos there. Many musicians upload their music mostly on YouTube. Then a private copy is allowed. However, some users may upload videos of which they do not own the rights. If a music video is uploaded by a person who does not have the rights to it, you will not be charged with the download. As a user of YouTube, you can assume that YouTube provides unquestionably legal content and deletes illegal content. So here you are on the safe side: If you download such a piece of music, the hypothetical guilt lies with YouTube and not with you.
YouTube Terms & Conditions
YouTube's Terms and Conditions states that downloading videos is not allowed or allowed. If you are not logged in to YouTube, you have not agreed to the terms and conditions. As a logged in user the download is strictly prohibited by the terms and conditions.
Still, you do not have to worry. No agency in the world would bother hunting for downloaders of YouTube videos. Because the videos are available for free, there's no financial damage to YouTube.
About this converter
The converter offered does all conversion operations for your download in-memory. Therefore, no data is stored on disk. Technically you are streaming the video and each download link can only be used once.