This proved very useful on our recent visit to Paris.
Only thing I would look for as an improvement is that it not only tell you the line to take to get to your destination but also the direction to take on the line. This can be confusing to figure out on ones own As it requires you to trace the line map to determine the end station in the appropriate direction.
Other than this one wish it is a most excellent tool to have with you in Paris.
Bon voyage mon Amis!
Grant Millard about Metro Paris Subway