Those are junk.
I have that exact one and it doesn't actually have a GPS receiver in it at all. It just uses cell tower triangulation.
Also, when you send it the SMS to get it's location it doesn't send back lat/long as the advert says, it sends you to a Chinese website with a cut down version of Google Maps that doesn't have any mapping data outside of China.
Save your money and get a TK102 based system from a reputable shop