My best arguement against using an essay service:
One of my most harrowing interview moments was during my blind interview at everyone's favorite blind-interviewing UC:
We had been talking for a very long time, I reiterated the vast majority of everything I've ever done, thought, and considered in my entire life. When the interviewer asked me:
"Now, are you SURE that when I go back and read your application it's going to reflect everything you've told me, and the person I've met today?"
For whatever reason I didn't expect this question (had never heard of SDN at the time), and it totally caught me off guard. And I'm certain that I would have totally crumbled had I had some professional re-write my essay for me. However, having plugged through my essay by myself, with proofreading by friends and family, I was able to confidently tell him that I didn't think he'd be in any way surprised by my wishy-washy GPA, the typo in the second paragraph of my personal statement, or my fairly pansy explanations of some of my extracurriculars.
Trust your ability to write, they really just want to get to know you, not you filtered down through some fancy metaphors.