Pros
Work schedule is generally afternoon to evening (3:30-9:30 pm) which leaves whole morning free. No unpaid or unexpected overtime unlike most Japanese companies. No out-of-work duties except training and yearly meetings, which are paid. Transportation to and from work is paid. Steady salary is not affected by number of lessons you have. Teachers are not expected to 'sell' lessons or pressure students into buying packages. Lots of training provided, with personnel always available by phone or email to take questions. Extra training or advice is always available. No need to make your own teaching materials or design your own lessons, but teachers are free to adjust games and personalize the classes for their students' needs. Teachers are never required to buy the teaching materials or supplies. Teachers are not docked pay for losing materials. ECC will co-sign for your apartment, but it is not mandatory. You are free to live wherever you want, there is no company housing. Semi-formal/business wear required, but full suits are not mandatory. There is no uniform. The dress code is traditional but not as strict as many Japanese companies. Salary never drops from year to year. A long-standing General Union is available for all teachers to join, and they actively work to secure better livelihoods for teachers. If you are worried about the business practices of large eikaiwa, the Union would give you great peace of mind.
Cons
Raises are negligible, a few yen per hour (average is 15) per year. No bonuses. Some people receive a 0 yen bonus. ECC does not pay airfare at any time. Salary is the same nationwide, so living in Tokyo will be far more expensive than in Nagoya or Osaka on the same budget. Very little opportunity to advance in the company. If you speak Japanese fluently you may have a chance to become a member of Personnel, but I believe their salary is the same as that of a teacher. Exceptional teachers may become trainers, but again I believe their salary is about the same. There is no opportunity to become a school director or anyone in the business part of the company if you are not Japanese. Upper management is all Japanese. Upper management often complains that "foreigners are lazy and overpaid". This is a cause of some friction between the Japanese and non-Japanese sides of the company. A lack of communication and cultural incompatibility can cause issues with policies and rules (for example, in Japan it is normal for bosses to demand unpaid overtime. In the US this is unacceptable for people being paid hourly with no bonuses and no recompense for their time. This results in workers being unwilling to do what they perceive as being taken advantage of, and the management sees this unwillingness as lazy stubbornness.) Dress code may be too stifling for people unused to traditional Japanese office structure. People who are unfamiliar with Japanese work style, hierarchy, paperwork, redundancy, roundabout communication, avoidance of conflict, unwillingness to discuss issues of importance, obsession with politeness etc. will have a learning curve when trying to settle in. Salary is enough to live on, but not really enough to save or travel on. Households or couples with a dual income will usually have enough to travel but you will have to live very frugally in order to save. Company is far more interested in making money than actual education or listening to the opinions of the employees. However, this is not nearly as bad as some other eikaiwa.