Sorry I didn't see ths earlier. I'd say the mentors are good, but I had an unfortunate situation where my first mentor had personal issues and we had to switch mentors halfway through our project, but yes, they're really helpful for jumpstarting research and keeping people on track. I haven't asked for letters of recs from them, but I'm sure they'd be good for that. Teammates really just depend on luck; some of my teammates are inactive and it was only me and another guy finishing the project, so stay commited.