Every published author on earth works with an editor. You are not above that. It is not cheating, and it is not a confession of bad writing. It is how writing gets good.
Doing it yourself has real advantages. The voice stays yours, which matters more than people think. You save money. And the revision process forces you to actually think about your story, which is painful and useful. The problem is blindness. You cannot see your own cliches because you wrote them. They feel natural to you. To a reader, they are the same phrases from the same thousand essays.
That is exactly what an SOP editing service is for. A good editor finds the paragraph where you repeat yourself, the opening that says nothing, the humblebrag that lands sideways. What no editor can do is conjure a better story out of thin air. If your experiences are thin, the polish just makes the thinness shinier. Editors polish. They do not invent.
So here is how I would order it. Write the draft yourself. Revise it twice. Run it through a statement of purpose checker app free tier, or any decent SOP grammar and structure checker tool, to catch the obvious mechanical stuff. Then hand the near-final version to a human. That sequence matters more than which SOP review service you pick. Paying a human to fix draft one is a waste of money. Paying a human to sharpen draft four is one of the best investments in the entire application.
Draft one is for you. Draft four is for them.