The service is great, and I have ordered plenty of pages from them. However, as one of the reviewers pointed out, many writers simply don't follow the guidelines. It's like you tell them something specific but they insist on writing something general. This is a shame as the quality of writing is very good.
Regardless of the cons, I still feel that this site is reliable and useful for proofreading. Also, if you are not happy with the paper they will edit your paper again free of charge so that's a bonus.