sorry, haven't tried it. but, what i DO recommend is to use the Princeton Review
online essay grader. it's $6.99 for two essays(analysis of arg, analysis of issue). If you don't want to purchase their whole online course, talk to them about getting just the essays. It's not a listed product, but I asked and they hooked me up. I did some essays and the feedback was useful.
800score.com also has good essay prep. check it out. the key is to follow the formula for each type of essay. once you get that down you shouldn't get anything less than a 4.