I almost always use this fx and use the dropper tool to try to click on something close to 18% gray. But invariably the whole scene goes much darker verses the color balance being just better. Am I doing something wrong?

Do you try to adjust anything else? When I use the ColorFixer tool, I almost always have to adjust the Brightness and Gamma, sometimes the saturation.
It's a great tool but takes some playing with to get the right color adjustment and exposure.

O yeah i bump the brightness and mess w the gamma but invariably the first thing it does is darken everything

It helps me to click the "reset to none" under prefs, then I start adjusting. It works good for me, just a little quirkiness to work around.

It also sort of depends on the image and how many darks are in the image. But drop the Film Gamma to 0 and it should be close to the original brightness. I like the way the blacks are affected by the Film Gamma, though.