I bought this because my smartphone's GPS was inaccurate, but this product also has about the same level of inaccuracy. It seems to be a Google Maps issue, so I stopped using it. I've attached screenshots of both devices taken about a minute apart. The smartphone moved slightly, but this product hardly moved at all, so I believe its accuracy is reliable. Please understand that the back is dirty before bidding. To keep the price down, it will be sent via post. You can also upgrade to Yu-Packet Plus for 300 yen.