This application will only install drivers from repository.
In your case nvidia-detect suggests nvidia-glx.
Did you install your current drivers by sgfxi, or maybe manually?
I suppose I'm too late now to say that you need to be certain before you change the drivers: I don't know what's going to happen when you change drivers.
The purpose of the application is to facilitate easy driver install for inexperienced users and a virgin install of a Debian based distribution.
If you haven't already changed the drivers, I'd like to see what nvidia packages you have installed now:
On the other hand, for me it's very important to know what the results are if you do change drivers...