Pros
The fastest, cheapest route to licensure. I decided to become a teacher in May, had a classroom and a full paycheck in August, and am now fully certified. In my experience, most of the fellows who made it through the summer training got jobs, made it through the next school year and received certification. I know some of the reviews here say you only have a 10% chance... that is too low, I think. At my summer site, about 55% of the fellows made it through the summer program, and about 80% of them got certification... so that's about a 44% pass rate for everyone, and if you don't count the ones who were clearly not cut out for teaching and dropped out early on, that rises to about 60%. Not amazing odds, but way better than 10%. I should note that my site had the highest drop-out rate that summer, but I think the ones who made it from my site did better the following school year, so I think these percentages are pretty close. You will meet some cool people and learn a lot about teaching... different things than you would learn from studying education.
Cons
The summer academy is really intense, and if you're making a lot of sacrifices to go through it, it's a big risk. About half of the fellows at my site dropped out or were cut during the summer, some on the very last day. I made it, just barely in "green," but it was the worst 6 weeks of my life. I was constantly sleep-deprived, stressed and anxious. There's some luck involved in terms of who you get as your site coordinator, your coach, your students, etc... and it stinks if you get dealt a bad hand and fail because of it. Some of the TNTP staff is really nice, but sometimes I felt like they were mocking us for struggling in the summer program when they had no idea (or had forgotten) how grueling and scary it was for us. Not sure whether this should be a "Pro" or a "Con," but a dirty little secret... you can end the summer on "Green" (pass) "Red" (instant fail if you go too far into red at any point to come back out) or "Yellow" (they'll think about it.) Basically, if you end on "Yellow," they'll pass you if you have a job lined up and fail you if you don't.