My advice is similar to the advice I would give regarding management consulting, marketing research consulting, etc.
1) Would I recommend the use of a consultant?
Perhaps, but it really depends on which consultant and what sort of help you are looking for.
2) Some are pretty expensive . . .
True, some are comically overpriced relative to the help provided and the level of service you receive. Then again, some provide exceptionally valuable advice. I think that it is important that the fee paid vary with the amount of work required for your application portfolio. A set of essays for Student A might take a few hours of review work while the essays for Student B can take three or four times as long.
3) I am afraid of a manufactured feel . . .
The best consultants will provide advice and research. They will NOT write your essays or dictate the tone or content of your application.
Hjort