Brainworx solo (Plugin alliance) use for mono?

The Channel Tools plugin bundled with SONAR will do everything that one does, and then some.
 
To check mono-compatibility, just click on the interleave button on the master bus and set the interleave to mono.
 
What plugins such as the brainworx one are good for is comparing what parts of the mix are going up the middle versus sitting out at the sides. That'll give you an idea of whether your mix is wide enough, and whether the low frequencies are in the center where they're supposed to be.