Dog GPS tracking System Legit?

Does anyone know if dog GPS tracking system collars are legit? I saw some at the pet store the other day and I must say that I’m very interested. I live in an area where cell phone reception is hit or miss so this might leave me out in the cold on this one. I could really see the benefits of having one of these pet GPS tracking devices though. I like to go hiking a lot and it seems like my dog runs off a lot. It would be great to know where she is at all times. I thinking that this will probably not be an option though since I don’t have very good cell reception.