First off, take a look here where courses have been reviewed by former students: http://www.teflcoursereview.com/courses/type/online-courses/

This type of course is for new teachers in entry-level jobs (as are most online courses). A CELTA is a high-end qualification which I'd only advise people to take if they've got a few years experience as its very intensive and demanding. Maybe after you've taught for a few years and learnt the basics you can go for a CELTA?