I worked with accepted.com
and in particular Cindy Tokimutsu, she is good but really she only edited like 15/20 words from my HBS essays..i was pissed so i had sandy HBSguru do a free eval of my HBS essay..and he really didnt have much to say..but he was nice enough to do a mock interview prep with me..and boy he really helped me out a lot..Cindy was great in terms of addressing my concerns i had when i was writing my drafts, i was just paranoid so i guess having her look at my work was very comforting. Cindy came highly referenced, my friends, a Booth graduate and another HBS grad had used her services before.
I had totally messed up my kellogg interview but with HBSguru's feedback I was really able to polish my interview skills..keep in mind, I had not interviewed in over 10 years..especially some BS interview process such as an MBA admissions interview. anyways end results..I had awesome interviews at HBS and Wharton.
As for $$$, HBSguru did the interview mock for free.. and Cindy charged like a total of $1000 for HBS and Wharton essays...
My take on using consultants is, do your own ROI, you still need to do your work and stay on top of the edits with your consultant, if you are like me..there wasnt much of any ROI, but HBSguru was very useful..and he was free!!!
If you are really struggling, go with an admissions consultant..they are the MBA's dirty little secret.