How are you playing your precious MONO Vinyl?

@elliottbnewcombjr How would using a stereo cartridge on a mono record damage the record? I can see that using a mono cartridge with no vertical compliance (eg Miyajima) on a stereo record could cause a problem, which is one further reason why I converted the Ruby 3: it retains it's vertical compliance but produces no signal from such movements.

As for the Beatles, I have my brother's original Parlophone mono releases, and have only ever played them with RIAA equalisation. I don't know if they were recorded that way, but they do sound fine.

I had Steve Leung of VAS convert an older BM Ruby 3 stereo cartridge by rotating the former holding the coils 45° and connecting the horizontally sensitive coil to both outputs. He removed the disconnected coil and put a new stylus on it. This was a lot cheaper than buying a new mono cartridge. But back to the original question:

Is EQ-100 or something similar, absolute necessary from a purist perspective or should I take the pragmatic path and use the ‘Mono’ switch on my Integrated with a built in phono?

If you have a true mono cartridge there is no need to use the mono switch on your integrated amp: each channel is receiving exactly the same signal, so it should make no difference. As to whether there is an advantage to using a mono phono stage, that is a matter of the relative quality of the phono stage you use now versus the proposed mono stage, but I don't think there is a reason to say that a mono phono stage is always better than a stereo stage used with a mono cartridge. If a purist approach is to be taken, with a mono amplifier and a single speaker, it would conform, but that involves a whole separate system and I don't think that's your intention.