Might want to add an arrow or notch to make your point a touch clearer, but otherwise this looks great. I've used a slider before.
The reality is obviously a lot more complicated since there are things that can raise BOTH, but this metaphor is great for the basic concept.
@aaronpk One should always be able to crank it to the level needed, with descriptive information about the implications and usefulness of the current level. One should also regardless of the current setting be able to manually set individual settings, with visual feedback on the information panel.
One thing that annoys me very much, is that you can’t set regular OSes to always download and install system updates automatically as they are known to the system.
You could even maybe illustrate the tradeoff for individual services and features. Everything has a potential for a score of 0 in Usability, but certain things with a higher usability score would decrease the maximum potential Security. So it's good to aim high within that range.