It works and the price is right.
It is an interesting concept: being able to visualize phase issues in the frequency domain.
I just tried it on the master buss to see if any frequency-specific phase issues were happening on my recent song mix.
The entire graph stayed in the positive except for a brief moment when I observed a slight negative around 200 Hz.
The 200 Hz region can have a lot going on, so it is not surprising to me. The small negative dip was so quick that I am not very concerned about it.
To verify that the plugin is actually working, I placed the plugin "Channel Tools" on the bass guitar sub-group.
I flipped the phase of the "right" channel on the "Channel Tools" plugin. The Correlometer display immediately displayed negative bars on everything from 20 to about 200 Hz. This was exactly what I expected to see.
I tried flipping the phase on one side of the drum buss and got the negative bars on the lows and the highs, where the majority of the drum sound was coming from.
The Correlometer seems to be doing its job as intended. I need to try it on many different mixes, including commercial releases, to get a good feel for what the display is telling me and to learn when I should make adjustments to the mix based on what the display is telling me.