I like that they proofread for me! They gave my paper back in less time than other companies who charge more per page, so it was really good value at £4 an hour compared to $9-10 /page by some others (and you'd be spending hours doing this work).
The turnaround times aren't great - sometimes days not minutes is what happens if there have been any edits or changes made since their last version but its still better then nothing from another editor when working alone which can take weeks depending upon how many revisions need making etc.