I'd agree that the 4 week on-site course is far more beneficial than the online course, but for teaching in China it's not necessary to get a job there. I've been teaching in China for 3 years and I see completely unqualified teachers arrive every month. One school I was at even faked a degree for one guy who had barely graduated high school, let alone university! China are always desperate for teachers as the retention rate for good teachers is quite low in most schools.
A good TEFL will help you enormously in the classroom, though, so they're worth it for that alone.
Be aware that the south of China is extremely humid from May-September. I only managed a year down south before I fled to the (slightly) dryer climate of the north!
Working in China is a mine-field. Most private schools put profit above education and treat FT's as a money-making resource rather than a teacher. Good schools do exist, but they are in the minority, I'm afraid. Do your own research about the school you're going to; I'd ignore places like Dave's (pro-China) and ESLTeacherboard (anti-China) as the reviews on those places are heavily biased one way or another. Best thing to do would be to ask to speak with a selection of current staff at the school you're going to in order to get an idea of what it's currently like to work there.
A good person to help you with getting started in Asia would be a recruitment consultant, I've always used gold star when I've wanted a change of scenery, email jim.althens[@]goldstarteachers.com and he'll be happy to help you. Do your best to avoid Disney as it's being pushed a lot here at the moment; a friend of mine (and a very good teacher) walked out after a month because he spent more time singing than he did teaching!