You will do another Masters degree if you go through Teach First and you commit to a set number of years, but a plus is being able to also do a year in industry too. Depending on your degree classification and subject and what you want to teach e.g secondary maths, Primary languages etc, you may get paid more (bursary) doing a traditional PGCE, (although some PGCE encourage you to take at least 30 credits at master level.) Carefully look into it as the PGCE route isn't always uni based as many schools have been given the option for 'direct' candidate selection where they actively advertise for trainee teachers rather than you aplying to a uni. You can either go on the DfE website for a list of schools directly advertising or check the recruitment section on the websites of the schools you would like to work at to see if they have any advertised places. Good luck ;)