Informal poll: is it within a teacher's rights to forbid the use of such a service on their assignments? You know, "I want to see YOUR work, not an underemployed English major's work." If I were a teacher and I thought my wealthier students were turning cash into better essays not thru tutoring (learning) but simply paying someone to spruce it up, I'd do what I could to ban the practice. It's not fair to other students and it makes it difficult or impossible for a teacher to accurately gauge a student's own skills.
Teachers consider the practice you describe (paying someone to spruce up an essay) cheating, but it's not clear that that is the kind of service that OP's site offers. Many teachers also encourage students to get critical feedback on their essays, and so they should. Many professional and academic writers seek out the same kind of feedback. I share your desire for the democratization of online education (that's the point of essayjudge) but there are so many sites that appeal to the baser instincts of struggling or just lazy students (selling pre-written or custom written essays) that I think any site that provides legitimate feedback to students, even if it's for a modest fee, should be welcomed.
I'd say getting feedback from an unbiased teacher is not much different than getting feedback or recommendations from parents or friends. Paying for someone's time that will help you improve your skills and do better in school does not seem unethical to me.