They tend to be on the high end of medium when it comes to cost but have a quick turnaround. However, scribendi reddit users know the quality of their work. It seems to vary across the board.
They were there a decade ago. I have not used them since. They were quite good. However, the anonymity of the editors makes it difficult to build a relationship with one editor. You are assigned someone randomly and have very little ability to communicate.
Fiction was a mixed bag. The editors I received (which had assigned numbers) were not very helpful. Some editors got what I wanted, while others didn't.
I decided to stop using them because I wanted to build a relationship with someone who understood the world, was willing to work alongside me, rather than just edit, giving me a vague response and then moving on.