in my experience of them, the quality is rock bottom, they dont last long, you will never stand a hope in hell of getting any form of warranty when they do go wrong, and they often do not perform as they should or have incorrect internals so off the shelf chips may not work.

the best option is to buy from a reputable dealer, who will give you a good quality unit that will work and last, face it you will end up buying one of these in the long term anyway, so it is much cheaper to do it now rather than later