FYI, plural eyes ONLY works when the quality of the sound recorded via the on board camera mic is good enough and its 'focus' the same as the audio you wish to sync to. So, in a quiet interview situation where primary audio is being recorded double system, sure the camera mic is perfect for lining up waveforms via something like plural eyes. But if you are in a noisy situation and the mixer is booming, chances are the camera mic picks up way too much ambience; or when you wish to sync up wireless lav sound on subjects and the camera is likewise too far away or the environment again too noisy, it will not work. How can it? Plural Eyes is 100% dependent upon lining up similar waveforms between the canon audio and the 2nd system audio; if they aren't there, it can't line them up.
Other than that, I use it constantly but ALWAYS have other fallbacks for obtaining sync such as getting the TOD clock as close as possible to the recorder TC; and slating when possible. A more $$ solution is to have a jam or wireless TC system, but this usually precludes also having a camera mic ( that is without adding a lot of stuff to the camera...).
my 2 bits