Pros
WIll get you a visa to work in Japan. Some coordinators are helpful. But if you try to leave, they will pressure you to stay, and expose some shady tactics to presuade you.
Cons
So, salary: When you apply, they give you a number. Later you find out: About 10% of that salary is a "bonus". A bonus? yes. They will deduct pay if you're late or absent - even with a doctor's note (on top of not paying you for the sick days themselves). You will pay your own transportation. You will have to literally TEXT THEM EVERY TIME YOU BOARD THE TRAIN TO WORK, as if you are a 5 year old. They are keeping you in a constant state of silent terror to show their dominance - playing with your mind and money. Go there only if you can't get an ALT job anywhere else.