Pros
Get to live in Japan. An easy job to get. Very supportive in getting you in and out of Japan. Very supportive in helping you with life in Japan. It's an easy job with lots of downtime and very little skill required, except the ability to speak English.
Cons
The company pretends to care about mental health. (You will be asked every year to fill out a stress survey. If you get flagged, you will get a consultation where they will tell you to get over it.) Very low pay, with a pay rise of next to nothing every year, which gives the impression they are just doing it to tick a box, so that they can advertise yearly pay rises. No career progression outside of becoming a Head Teacher for a tiny pay rise, unless you devote yourself to becoming a native level Japanese speaker, and even then, I have never seen or heard of a non-Japanese staff member in this company outside of instructor managers. The downtime can get very excessive at times, and you may have to try your best to find something to occupy yourself with.