I am rather a skeptical person in terms of if "something sounds too good to be true". However, in this case Ninja Teacher do deliver!
Everyone on here has told you how it prepares you for actual practical living in Vietnam, aswell as teaching. So I do not want to dwell on that as it has been said.
I will comment on the fact that Ninja teacher gas such extensive contacts in the ESL teaching field, in Vietnam, that it can easily help you find recruitment. I myself found recruitment through a Ninja Teacher connection and I couldn't be happier with my choice if company and job. I have talked to several teachers who did their TESOL online or through some next academy, and they are not working for the best of companies or schools. Thanks Ninja!