TL;DR Proofing excellent, line editing, not so much.
I used Roxana for my latest, sending it to her after a first line edit and proof had been completed. I opted for the line edit, because I wanted to see how good a line edit you can get for $50! My conclusion is that I will definitely use the service again for a proof, as Roxana uncovered an additional handful of typos in a 90k word book, which is great. I wouldn't use the line edit again. There were a few suggestions, but I rejected all of them. I did end up re-writing one sentence, just for clarity. One of the line-edits made a suggested change to a Shakespeare quote! That did make me wonder if a program, rather than a human, was involved.
I will certainly go back for another proof, as this is great value.