I received an offer to be a Carnegie Fellow in Baltimore in the first year of my postdoc at Berkeley, but ended up waiting a year to get a faculty position given my advice from my mentors. I had just published one paper and I was almost finished with another manuscript, so I thought I would be ready for the job market anyway. So in the end it was good for me to wait.
I was actually pretty excited about the "glorified postdoc" position because it would give me lab space, a faculty mentor(s) and a lab technician for 5 years. I also would be able to interact with all of the Carnegie and Hopkins faculty, so I knew I wouldn't be isolated. I didn't think I had to worry about anything except to do good science and be creative! And everyone who had been a Carnegie Fellow, had obtained a faculty position.
The only thing that held me back from taking the position was the 5 year stipulation. I knew from the advice of my mentors that my research would already get me a faculty position in less time. And they were right. In hindsight, I would have loved to spend more time as a postoc doing more lab research, especially the live imaging that I love to do, than more of the paperwork/office stuff I do now. But I love my job, research and I'm really happy making a difference in student's lives.
I think these positions are fantastic if you are just starting but I was far enough in to my postdoc that the time to faculty position was a deterrant for me. I also would have never ended up in the faculty position I have if it wasn't for the time in which I was applying. They were looking for someone with my expertise and background just at the time I applied. So as fate goes my decisions not to go do a "glorified" postodc route was good. But if I was at another time in my career, I would have been an honor to have this experience, money, lab, mentorship that comes with these positions.
Just a note about this "glorified postdoc" position: I was actually asked at my poster at a meeting to apply for this position from Carnegie faculty. I learned from this experience of the power of a good poster and attending meetings, at the postdoc level or any level for that matter. It's all about the marketing and networking.
I was a Lewis-Sigler Fellow at Princeton and really loved it. The best part was the independence, environment, and resources. I was able to develop my own research program, run a small lab (techs, undergraduates, and visiting professors), start substantive collaborations, and teach. It was like training wheels for being a professor, which made me feel a lot more ready once I moved into a tenure track faculty position. What I didn't have to do was write grants or do a lot of service work. The nature of the position was such that I could "round up" when I wanted to, like to meet with seminar speakers or be a full participant in developing curriculum, and "round down" for responsibilities I didn't necessarily want. Managing a bigger lab and being a professor has still had a learning curve to it for sure, but I'm certain it would have been harder coming from a traditional postdoc. For example, I came in with a reasonably good idea of how to hire people and how to manage a budget. Money-wise personally, it was also pretty great to have a near-faculty salary instead of a postdoc salary.
However, I definitely don't think it's for everyone. I agree with Ahna that it may not be the best use of time if you are already immersed in a productive postdoc. I started my fellow position right out of grad school, so the timing was good for me. I also continued/expanded in the same field as my graduate work, and if you want to change fields, you really need to have a good plan for how you will gain the skills you need (like through collaborations with local labs). Even staying in my same field, it was very useful to join a local multi-lab group meeting where I could get feedback from other people. As for mentoring, I was a special situation because I moved to Princeton coincident with my graduate advisor, so there was a pre-existing relationship to build on, but I also worked to find other mentors. I think this was very important, both for my science and for my career. I felt like I got pretty good mentoring, but you have to be proactive to make sure that happens. Also, it's worth thinking about whether you really want to run your own group as a postdoc. It's a lot of responsibility to have people working for you, and you need to have a well thought out research program. You definitely have enough freedom to fail.
Maitreya's answer is essentially perfect!
The only thing that I would add is that, in general, the best candidates for these positions tend to be deciding between taking a tenure track position directly after graduate school or a "fellows" position, not choosing between a "fellows" position or a traditional postdoc.
I was a QB3 Fellow at UCSF for two (fantastic) years and then took a faculty position here.
This forum is designed to provide a safe and helpful space for academic career advice and mentoring.
We reserve the right to remove questions and comments that are aggressive in nature or use inflammatory/insulting language.