Teach first is a 2 year programme working in challenging schools. You get a couple of weeks of training ans then get thrown in, which has pros and cons.
In my experience they can be a mixed bunch between normal trainee teachers, people who do it as a stop gap to make their CV look good (so have a place on a grad scheme on hold) or ambitious people who chat the chat and somehow end up in senior leadership within 5 years.
The teach first schools near me are staffed by up to 50% teach first staff (usually because there are issues that mean experienced staff wouldn't touch & thry are also cheaper than getting a more exlerienced teacher).
At teach first you cant guarantee your location or your subject.
I think they are good at developing very confident, ambitious teachers. I think sometimes their story can be a bit like 'we are the best and we are saving children from all these crap teachers'.
The main benefit i can see from TF is that there's a massive network with big wigs and people seem to end up with lots og fingers in pies e.g. go off to work for a political think tank with 36 months experience.
The scholarship is a more traditional route I think. Sometimes the traditional routes can have their teaching methofs still glorifying discovery learning etc. The schools are usually good or outstanding (though both have their challenges). You are more likely to have an experienced colleague as your mentor on that route I'd say.
If TF could have guaranteed my subject and location then i would have done that route. I did a traditional PGCE in the end.
I think it depends what you want from your training year.