Like Zaikesman, what I've read and been told over the years is that using the mono switch is all that's needed to mimic the operation of a mono cartridge. I can't vouch for its accuracy, but below is an explanation I found on another forum; maybe others will know if it has any merit.
"A stereo phono cartridge has generators that are sensitive to 45-degree motion corresponding the the 45-degree groove walls. It is wired in such a way that lateral motion of the stylus is in-phase and vertical motion of the stylus is out-of-phase. Therefore, when you blend the channels with a mono switch, purely vertical motion is completely canceled and purely lateral motion is maximized. This is exactly the way a mono cartridge operates. There is absolutely no difference whatsoever."
I also like using a stereo cartridge for mono records because my preamp allows me to send either the left or right channel to both speakers. On a few of my mono lp's, one groove wall is damaged much more than the other, and a stereo cartridge lets me listen to the less damaged wall.
And of course, there is the promise on the album jacket of many of my mono records that when played on a stereophonic machine, it will give "even more brilliant, true-to-life fidelity" than when played on a monophonic machine.
However, also like Zaikesman, and for the reasons listed above, I've never tried a mono cartridge in my stereo system, and none of the local dealers have a mono cartridge mounted up to audition. I greatly enjoy my mono records with my current setup, so the expense and hassles of adding to my system a turntable and cartridge dedicated to mono is not one I would undertake lightly.
