Pros
Small classes with wide variety of age-groups The kids are (as always) absolutely adorable. I love my students. Pre-made lesson plans Social insurance, health insurance, housing, and taxes are all taken care of A lot of time is spent with your immediate co-workers (in your school) which, if you like them, can be a huge plus. Contract signing bonus has never been threatened. I always get it in full. I have had nothing but positive interactions with any of the Japanese teachers that I have come in contact with.
Cons
If a student leaves, for any reason, you will be told (or it will be suggested) that you are a bad teacher. Same if a demo doesn't sign up. All the blame for anything in the school, is placed on you. It may not be said angrily or as bluntly as that, but it does wear on you with time. A lot of decisions made by head office make sense on a large scale, but can often be detrimental to schools that are outside the norm (outside of Tokyo). There is, theoretically, a cover-teacher program but if you live outside of Tokyo, it is unlikely that you'll be able to use it unless you are gone for an extended length of time. The new promotion system (which has changed three times in the five years I've worked here) seems to be purposefully murky, unclear, and difficult. There is miscommunication about how it works between almost all levels of the company. However, if you don't plan to work at Winbe for more than a year or two, then it isn't much of a problem. Miscommunication happens frequently. Rather than having a Native English branch of management and a Japanese branch of management, like they used to, it is now all under the Japanese branch. This means that important information about company management is often relayed only in Japanese. Because so much happens at individual schools, what your experience is like will be much like a lottery. Maybe you'll have a great experience at your school (I loved my school), or maybe it'll be terrible (some of the teachers I contact have that experience).