The hours are rough, at least for in person fellows, it could be better online.
You get one personal day, so if you have an emergency and need to be off work for anything except you being sick, you're hosed.
Fellows day to day is largely controlled by the school they're at, not blueprint. That means if the school you're with is not used to fellows and doesn't have an established program yet, your schedule will be chaos.
If you are in person, and your manager is not there's just not a lot of support they can give you even if they try.
The pay is bad. I understood what it would be before I started, but it didn't sink in for a while that I was making less than I could make with a part time job at Target, while working 45 hour weeks.