Why are there two plug-ins called xxxx(Mono) and xxxx(Stereo) installed ?
“Mono effects” (which are effects that do not make any difference between left and right channels) are bundled this way for performance reasons. Some developers just deliver a stereo Version which also processes (twice) mono streams. The “(Mono)” plug-in is to be used with mono streams, and the (Stereo) one with stereo streams. The effect itself is the same in both cases but the number of processed channels is different: this may drastically improve performance for CPU intensive plug-ins.