Vantaggi
They usually pay on time. The materials are prepared by the company. Teachers just need to review the materials and add their own supplementary materials at their discretion.
Svantaggi
There is a lot of administration work, the most tedious of which is making student reports a few times per term. Also, depending on the branch, you might have to work weekends. I have worked for several branches, and my current branch is easily the best. At the other branches, teachers worked most weekends. Getting red days off was like pulling teeth. When I was at one of the largest branches, we had to work two out of three days during Chuseok and Solnal (Korean Thanksgiving and Lunar New Year). Management then got mad when teachers complained, and tried telling us that we were getting 2 days off. They were counting the number of hours, while the teachers were counting days on the calendar, as any reasonable person would do. Teachers were also treated very unfairly. I was treated well, but mostly because I brownnosed and didn't stick up for myself when I knew management was taking advantage of me. Turnover was quite high. All I can say is, apply at your own risk.