Definitely a worthwhile investment

The Training the Trainer Course is more than just a course.

It will give you the opportunity to feel what being a teacher trainer is like by effectively doing the job.
Giving a model lesson, leading an input session, assisting trainees in lesson planning and giving them feedback will allow you to test your knowledge and skills and evaluate these critically.
Shadowing experienced tutors in teaching practice and input sessions is an invaluable way to learn how to approach teacher trainer courses and it fosters professional development.

For anyone who wants to work on training courses, the Training the Trainer course is definitely a worthwhile investment.