David for those people who simply cannot afford Teacher Training courses costing thousands, or the time needed to take of work to do so; or also like me have no good Yoga classes anywhere near them then home study of course is a good option. Will it be as good as doingTeachers Training in person with an organisation, very probably not.
Regarding getting sued it can happen in any profession, not heard of any of the thousands that have done home study in Yoga getting sued yet. Many people that teach martial arts, etc do a lot of stretching; I know a great many that have been teaching for years and have no clue on stretching theory or exact alignments and postures, many even do stretches regarded as bad for you (e.g. hurdler stretch - one leg out in front straight one behind like hurdling, head to knee; even box splits feet paralell sideways split is bad for knees, etc) not met any that have been sued. Virtually all stretches in martial arts and other sports can be traced back to Yoga or a variation of them.
Forgetting about certification in home study, what exactly would you advise for those that cannot afford courses costing thousands (Bikram, Iyengar, etc, etc) or the time off work to undertake them; and those who don't even have a good Yoga class at all near them? Without getting certified just home study course like the link above you would say is a bad idea? To do such a course then continue learning and improving by attending seminars or workshops with the best when opportunities arise, as well as more home study.
Every Yoga teacher on Earth has done some home study - have you met one that does not own a single book or DVD on Yoga, or does not buy magazines on Yoga? Many have had hands on training but they also learnt a lot on their own, no Teachers Training can cover everything to the point you won't learn anything more after it.
With home study people can learn a great deal, and more importantly decide if a career as a Yoga teacher is for them. At very inexpensive cost compared to Teachers Training with top branded Yoga companies, it means not investing thousands in something that you may decide is not for you after all to pursue, or worse go on a poor course and blow thousands on it.