I used EssayEdge once and I'd say that, overall, it's really not that impressive.
Granted, I had already edited my essay quite a bit. The most that I got from the critique was a few shortened clauses and a few esoteric vocab. words placed in random places.
It was actually a pretty funny story. I usually do well on essays, but I thought my essays weren't that great. Then the guy from essayedge e-mails me with minimal corrections and says I'm a great writer...oh well, I guess if they don't edit your essay, the money is worth the uplifting comment. 😀
Overall, I would say this: you know if you're a good writer. If you are a good writer, just write like you usually would and get it critiqued by teachers/writing center. However, if you struggle with writing, essayedge is great for editing your FIRST draft (no point in doing editing for them if you're already paying).
Anyway, that's my $0.02.
-Dr. P.