You can't be any worse than the same service that the Harvard weasels run (Essay Edge), but frankly, the worst waste of time and money that I encountered during the whole law-school application process was sending my PS in to those dolts for "professional editing".
The incompetent buffoon who "edited" mine made numerous grammatical and spelling errors in her changes, suggested deleting a key sentence about my knowledge of foreign languages, and included six pages of boilerplate drivel that was clearly written for someone else's PS (since it referenced topics that didn't exist in mine). Not only that, but the "service" also said that their editor would answer questions; I sent half a dozen specific brief questions, both to her directly and to her through their central email address, and never heard a word back. Then they had the nerve to ask me what I thought of their service ("it sucks") and whether I would recommend it ("no").
I got exactly one useful suggestion out of it (deleting a tangent), but it wasn't worth the hundred-plus dollars they charged. My sister-in-law came up with the same one, and I merely had to grit my teeth and thank her for it.
As a result, I really don't recommend using these sorts of services. Find a professor, TA, college prelaw advisor, and/or friend to help instead. At the very least, skip the services that tout their ivy-league credentials and go with a real professional in your local area.