Pros
It's a fast way to get your teaching certification and get into teaching. They attract an amazing cohort of fellows who come with interesting backgrounds, experiences, and stories. You would meet some amazing people at this program.
Cons
The program is basically a scam. The program gets income from two sources: government grants and sponsorship from charter school organizations. The charter schools also get government grants to run their summer school programs. You sign up to this program and give a charter school that you do not get to choose for weeks of free labor. They will work you like a dog. Expect a ten hour work day plus commute and frequently even homework. Don't think you'll get weekends off either. Some people have it significantly worse than others. If you signed up for a SPED certification that's more work. If they give you two lessons to teach per day, that's more work. How well you do in the program is almost completely random. You will be assigned a random grade to teach at a random charter school. Some schools have small class sizes (as little as 3 or 4) and some have huge class sizes (as much as 44 students in one classroom). Some schools have nice desks, clean white boards, and plenty of tech, others will have folding picnic tables, scratched white boards that don't erase, and whatever tech could be scrounged together at the last minute (and may not work). These differences are not taken into account when you are evaluated. Evaluations are also random. They happen on random days and at random times. The difference between passing and failing the program can come down to when your observer decides to walk in the room. They only stay for ten minutes and will grade you on parts of your lesson that they didn't observe. If you're trying to enter the field of education you probably already have an idea of what kind of teacher you want to be. You may have a vision of yourself as an educator based on the kind of educators that helped you as a child. TNTP does not care. They have a specific kind of teacher they want and expect to have a bad time if you want to go another way. If you want to see what kind of teacher they'll be making you go watch some videos from Uncommon Schools. Personally it looks like some kind of dystopian nightmare where students are replaced with robots.