I'm so sick of ALT life, I didn't reply before, but some of the tone here is a bit negative, so I need to jump in, to give a less bitter point of view.
You're best off finding Facebook groups to get active ALT opinions. Search ALTs there. For example, Sapporo City ALTs has 285 members.
I wrote a 40 page comic about the stupidity and incompetence of the ALT system, which I posted here in my main thread, "def in Japan", an easy search if you're inclined. My main thoughts are, teaching is something you learn through experience, not in a classroom. Training a 'teacher' for two years in a university is useless. Two years in a classroom attempting to teach does a world to show the flaws of a teacher and gives a roadmap to becoming a useful teacher. Unfortunately, Japan has no interest in maintaining ALTs long term, and I'd say they actively discourage it, through contract systems and meager pay. So, most ALTs are not competent. But it isn't because the they aren't trained. I've worked with first year Japanese MEXT approved teachers, and they aren't great either. Some things can be taught at university, teaching isn't one. It requires interaction with students. You can't simulate that.
I still think training is important, but having seen a lot of TESL certified teachers in my time here, I think one teaching hour is equal to about 10 classroom hours. More important is having teachers who want to teach, and not loads of fresh university grads looking to have a working vacation.