aerien
IMO, getting a consultant for the business school application process is akin to deciding if you want to take a course to prepare for the GMAT or the GRE. How much leg work / discipline do you have to go it alone? Do you need or like the structure of having someone support your process in terms of timelines for exploring school options, tackling the application, searching for that perfect essay topic, etc. If you want someone to help you go through that process, then you can search through a number of firms listed here on GC and elsewhere to see which would be the best fit (some focus on certain aspects of the application vs the entire application; some let you choose a consultant based on background, school you're interested in, or recruiting industry, etc).
Personally, I did not use a consultant for bschool apps, though I obviously did spend an inordinate amount of time on GC so take that for what you will.
What he said

I'll add a few things that I think we can offer if you are considering consulting
- Perspective: We've worked on TONS of applications from lots of different people in different countries and industries. We also have a team of MBA grads and other folks who have a combined experience both in applications and applying/attending themselves that is invaluable. We can tell you if your essays are boring, fascinating, tedious, and so on. Likewise for all your application materials
- Positioning - We can give you an honest evaluation of where you stand given the above experience and knowledge, and help you construct an application strategy around that.
- Storytelling - We help out clients weave narratives. Some people are amazing natural storytellers, others are not

- Writing - Likewise with the writing itself, we advise on how to make things more punchy and effective and unique in all application materials (although I wrote "writing" this can also be with interview prep, video etc.)
Structure and Support - We are here to answer you promptly and directly, to give your application and timeline structure, and to nudge you a bit when you fall behind schedule.
Ummmm there's gotta be some more stuff we do too, but that's a good start!
Jon