Gpx Downloader requires you to have an android device with USB OTG (USB Host) feature. It can download gpx tracks from such devices: Holux GPSport 245 (ver: 1. 05, 1. 06 and 2). Mainnav MG 600 and MG 950d. (and probably some others similar to this). Every time when you plug something in your USB port android asks what to do with this device.