Before you sign up for Rev, understand that you need to put time and effort into this before it is profitable. Once you do though, it's a perfect way to supplement your income, or make a tidy sum if working from home full-time.
I love working as a freelance transcriber. I have hundreds of files to choose form, I can pick ones that are interesting, and they give you ample time and direction to always get it done quickly and correctly.
I've heard that you can be fired easily for mistakes, but if you are careful and make sure to put in the effort deserved to get the file done correctly, you'll never have an issue.
Not only is Rev great because I get to learn a lot of things as you're transcribing University files, medical files, lectures, YouTube videos and more, but it's totally based on your time and when you want to do it. Just sign in, and work away.
I will say, Saturday and Sunday's are normally slower, so if it's just a weekend job, I'm not sure how lucrative that would be.
I did it full-time for a period of time, and absolutely loved my job.