[TL;DR - Alright location, seemingly strong benefits, okay culture, and cohesive environment; go in with a laser focus and talk up your skills and how they fit perfectly with everything you see and you'll be fine.]
I was contacted by email by a recruiter who found me via university career development. I expressed interest in a phone interview, and it was scheduled quickly and was straightforward--largely a review of my resume and selling me on the position. I expressed my interest in hearing more and was told I would hear back in a week if the process would move forward.
The next morning I was contacted again to set up an onsite interview at their headquarters. I managed to delay it to the next week (scheduling around another interview), so they are flexible that way. For those who live a substantial distance from the site, they will fly you out and pay for a car. For those closer by, they will pay for a car service to transport you. The process began with filling out an application. By this point, my name was being floated for both the management and design groups, so focusing my work history and experiences was highly non-trivial. I would recommend being prepared with references and phone numbers if you are recruited like this. I received a final itinerary for my day, including who I would meet and when. Each person was described with their role/background, as well as the university(ies) from which they obtained their degree(s), which I thought was odd. Each interview was scheduled for 45 minutes with short breaks in between.
The first interview was with an HR staff member who was not my recruiter (in fact, I never saw the recruiter all day). The content was another resume overview but was primarily discussing the position, to sell it like in the phone interview. Some questions here and throughout the day seemed like they were trying to see how much I knew about the program and the company already, but researching the role like this is impossible with their prerogative of remaining as secretive as legally possible.
I then met a graduate of the management trainee program, who was a current manager of a few supervisors in the warehouse area. He was pleasant, but highly interested in me asking questions at every moment. It was a hurried tour of the building, followed by a hurried interview. (In general, it seemed like the combined interview day was a bad idea.) I met with a design department manager (~10-15 years experience) next, who had a great perspective about design and team structure. He didn't delve very deeply into the types of work and functions that were performed by design/development training hires, so I left with a vague idea of the job basics. This was a pleasant interview, although I thought there was a huge focus on hard skills gained from otherwise-irrelevant prior experience (e.g. R&D) that one might expect when recruiting engineers. Not enough discussion of personality and soft skills, especially for a generalist position like that for which they appear to be hiring.
My second-to-last interview was a free lunch with two recent grads of their respective development programs. They asked some questions about my career goals, and I asked some more personal questions about the jobs they did (experiences with supervisors, day-to-day tasks). This seemed to generate mixed responses: some facial expressions saying "why would you ask that?" to seemingly innocuous questions and others seemingly congratulating me on the great question.
The last interview was a strange twist. This was with a director (if I remember correctly) who didn't look a day over 25 and had quite a pretentious demeanor. Questions began without any softies, to the effect of "why should I think your name on the recruiter's desk is worth anything?". Not such a great way to end. He asked some company-aggrandizing questions (worded hypothetically, but which I was meant to answer, I learned) about why the MMC business/free returns model works. I asked a few questions after about the business, trying to appease his ego, but was also eager to leave after my day. Generally, a pleasant but bizarre experience, with quite the punctuation from young-wünderdirektor.
I ended up not receiving an offer (learned a week and two days later), and I honestly cannot say I would have taken it if I had. It would at least have been an easy decision for me (given that I received my dream offer the same day as the MMC interview) but for those out there interested in this program, think long and hard about it. I had seen the reviews going in, and while they do appear exaggerated from my experience, it is a strange place with some highly quirky personas. Applicant Beware.