I have tested this application in my Nokia Lumia 720 and it has worked very well.
But I see I need to ask you a few comments:
Change the color of the track file GPX (green almost unseen)
Modify the saved trip file manager. Use the system of selection of WP8 files, (list) using touch on the left side of the screen. Allow multiple selection for deletion of multiple files.
Allow direct recording of tracks in gpx format. I have not found applications compatible with the extension. mnt.
The adjustment of the setting of the minimum distance of tracking, interval minimum tracking and, above all, horizontal minimum precision, using sliders is a little uncomfortable (especially in the horizontal minimum precision control, the values not can be adjusted exactly to your liking.
I hope that you understand my bad English (using Bing translator).
I wish that these ideas will help you refine your great application.
Esteban J. Millan commented
Sorry, in the previous post I wanted to say that I find no applications or programs of geolocation or Geotagging, compatible with the extension. tmt.