Vantaggi
As someone with a Master's degree in Biblical Hebrew, my employment prospects were not stellar. Working at Eteacher gave me an opportunity to use and develop both my language skills and my teaching skills. The number of hours were flexible, and the pay, while not stellar, was good for someone just out of graduate school. It was a great thing to put on my resume.
Svantaggi
The biggest problem with this job from the teacher's end is the "industrial" model of teaching employed. All of the lesson plans and materials are prepared for you, and all teachers use the same materials. This is a pro and a con at the same time. On the positive side, you don't have to spend as much time doing class preparation and curriculum development. On the negative side, you don't get a lot of flexibility in what you teach, and more importantly, the lower class prep time justifies a lower pay-rate. The curriculum is not flawless either. There are a number of gaps in the material and the order in which the material is presented is not always ideal. Your experience teaching the students themselves will likely be mixed. Most are adult learners with day jobs, and many of them realize within a few weeks that they've gotten in over their heads and will drop out. Others will simply not do the work and drag the class down, and since they are not receiving grades, there is not much way to motivate them. Recently, students receiving academic credit were integrated with the non-credit students, which was a big mistake in my opinion, since the level of motivation of academic and non academic students usually varies widely. In addition, there was an administrative change from a model in which teachers received 50% more pay for teaching academic classes to a model in which they simply receive a rather pitiful bonus for administering exams and grading assignments.