I'm in the process of using an admin consultant at StacyBlackman. I'd agree that it is difficult to solicit critical feedback from your peers. When I asked my coworkers to look at my essay all I'd get is "looks good" with some grammer edits vs. the admin consultant that not only looks at structure, but the best way to phrase your answer to the question.
It isn't cheap at all...but I'd agree with the comment earlier that if you're going to spend +100k (plus giving up your current salary) what is the incremental 300-1,000 bucks for a greater chance of getting admitted to a top program where starting salaries are 30-40k higher than mid-tier schools.
One last point, I think that I've done twice as much work because I have a consultant vs. if I did it on my own. They difinitely push you to put in the time. Coming from a +70 hr/wk job, I really needed this.
My take aways thus far is: It isn't for everyone (and I can see how some people might think it is a waste of money), but I believe that it is money well spent.
Hope this helps.
p.s. I'll be sure to update this with negative feedback if I don't get into any of my target schools.