Pros
The better options compared to other eikawas out there in Japan (unless you are in the JET program). It's an alright job if you are lucky to work with a good manager who's there to advocate for their staff. Otherwise, they'd be bowing to the management to cover their back. Health insurance -- what management won't tell you is that you are eligible for your medical cost reimbursement, except for OB/GYN, dental cost, and therapy. Everything else is subject to review and reimbursed so you are essentially paying ¥0. But unless you have a good manager, they're not being explicit (even borderline secretive about this).
Kontras
Everything else. They will find a loophole to deny you bonus and pay raise as much as possible, they force their Berlitz Method to everyone without exception, even the students themselves state that they want flexibility in the topic and teaching method, e.g. discussion, not so much repetition. You will need to be tact in navigating this otherwise they'll basically mark you down for everything that actually give them returning clients. Last time I heard they are taking away water dispenser from the teachers' lounge to cut expenses.