I could see the autonomy being hard for some people. Some people just like to know exactly what they need to do, the Drawboard I knew would probably be really frustrating for people like that. The high levels of trust also meant high levels of responsibility, times spent working were full and challenging, some people may have trouble finding that right balance.
At least while I was there, there wasn't much in the way of learning or mentoring, you were pretty much required to be good and have a pretty good idea of what you were doing before you started. I learned heaps from the amazing people I worked with, as we solved hard things together, but that being said, there was no hand-holding for your responsibilities, the small team meant that it was on you to figure our your part yourself. Not because of lack of empathy, there just wasn't anyone else above you that already knew the answers. Might be different now though, I could see a junior growing substantially under the guidance of some of the people I worked closely with given the chance.
