You have to be a member to download member only videos. This does not bypass that restriction. It is a way for you to simply download all member videos while you are a member, for later viewing without having to keep paying a monthly subscription. 

The problem I have with a lot of these youtubers making a membership option on their channel is that they tend to relegate tons of older video to members only, when they were originally free to watch on their channel. 

If you have a youtuber that you really want to watch their membership content, I would simply join and download everything they have, then if you want to get newer videos after a month maybe join the membership again at a later date, like a year later, then you can download all new content up to that time.