My boss and I both did it and got our category I certification.
We really enjoyed attending the clinic that was required and going through the process. I thought it was very educational and gave us a lot of tools that we took back to our students. I definitely don't think it is targeted toward people who go to horse shows over people who just instruct. I felt that it was geared mostly toward trainers of any level to be able to provide their students with better instruction, exercises and education whether at home or at horse shows.
I'm working on my certification. Just have to take the exam. I don't show much (2-6 shows a year) but am doing the TCP because I believe this country is in desperate need of a certification program for this sport.
The information is geared much more towards how to teach and train and less how to show and ride, in my view. I really enjoyed the clinic (Linda Allen/Geoff Teall).
I really believe that one of the best thing that our professionals can do for the sport at this point is to go through the process of getting certified. I very much doubt anyone would regret going through the process.