I interviewed there once and had a very bad experience. I was contacted directly by a Partner in Strategy regarding a mid-level position and had 2 fire chats with him and one with another partner. At the time I had 2 years in IB and was pretty well rounded in both interviewing and live cases. I was intrigued by the way he presented the firm - a very autonomous and very flat hierarchy. You can work on own projects which are supported (and encouraged) by seniors.
However, the people I met interviewing was horrendous. One of the interviewers was negatively biased from the beginning. Very unprofessional - and I suspect it to be because I said no to cake, and she felt offended or felt that I implied she shouldn't grab a piece.
I was told by HR beforehand that this was merely a fit interview but ended up getting a case anyways - fair enough...
The case was - at best, unrealistic, but the correct phrasing would probably be “ridiculous”. PE firm wants to accelerate top-line growth with 10x in less than 5 years - in a mature market where the target is in a duopoly. No diversification. No market expansion. Organic growth in the current market alone. I kept asking clarifying questions, but no new info, no help, no alternative to 10x rev in less than 5 years in the current market. I tried many different approaches, but in the end, nothing seemed to satisfy them. (the company just downsized their operation here 2 years later).
When I got the feedback call she told me that I wasn't creative enough, but failed to answer me on how to solve the case. Before hanging up, so told me that she now wanted to grab of fridaycake before leaving the office, with reference to the "cake incident" before the interview.
I've since heard more cases like mine - where you get completely unrealistic cases that are impossible to solve. So be prepared to think (A LOT) outside the box. Also, they told me that the arent looking for classic analytical skills, but are seeking facilitators. They have an article on their webpage (https://implementconsultinggroup.com/facilitation/) about this. I think this would be a good start for prep - I don't think "classic" consulting prep is particularly valuable here.