Mono switch on phono preamp vs Mono Cartridge

thanks, you are right, I think the question is then more general, comparison between a mono button vs mono cartridge, how big of a jump, or advantage does it have on playback.

And yes, basically looking at potentially , with patience and time: rb330 (used), hana SL mono (used) and Transrotor Arm Base. 

As it happens I have compared both ways, own both, use both and can answer your question.  The short answer is the button will give you about 60% of what you would get with a mono cartridge.  The button (at least my set up) is prone to a bit of hum, easily subsumed by the music.  The long answer.  Cartridges compared:  AT 33 Mono vs. AT 33PTG/2 and Ortofon 2M Black LVB vs. 2M Mono SE (the mono version of the Black).  For a button I turned to KAB.  I used my C-J ART Phono initially and then later my PS Audio Stellar phono pre.  For the AT cartridges I tried both with and without a Bob's Devices SUT.  For Line and power it was C-J initially and later Marantz.   The results were consistent with any combination of phono stage, MM or MC, etc.  If I were you, I'd buy a mono cartridge, I agree with @viridian that it would be best to match your Hana ML if possible.

OP,  Great question.

@billstevenson Great answer. 

+1

I am a big advocate of having a dedicated Mono Cartridge: pre-mounted with an arm with a removable headshell, or two tonearms. My left arm is Mono, ready to go in seconds during a listening session. 

I have a vintage McIntosh mx110z Tube Tuber/Preamp with a full featured Mode Switch I never want to live without

I played Mono LP's with Stereo Cartridges, Preamps on Mono for 40 years (I'm 77 now). (not vintage mono, I mean early 60's mono. I paid $2. for Mono or $3. for Stereo, and didn't have good equipment back then. Budget: $6./week, gotta decide.

I read here after I joined in 2019, and tried a true mono cartridge, and I am so glad I did.

The answer is: it is a little, a little more, a whole lot better depending on each LP.

a. always less noise, as any slight scuffs, minor warps, dust in the grooves will make some vertical motion which will be noise in a Stereo Cartridge, nothing with a Mono Cartridge: a little, a little more, a whole lot more noise.

b. precise distinction of individual instruments and voices. That's the whole lotta difference. NOT Imaging, distinction.

I have a mono lp with early Louis Armstrong. I played it with my AT33PTG/II preamp in mono mode. The whole thing was like a history lesson, I would never play it again.

I received my inexpensive Grado Mono, elliptical on aluminum:

https://gradolabs.com/products/grado-prestige-mono-phono-cartridge-model-me

Oh, there's Louis, now you can distinguish trombone, trumpet, sax ... I play it for friends, they usually go home and buy a Mono Cartridge.

It is hard to break the habit of seeking Imaging, and some Mono LPs benefit from listening thru only 1 speaker, which my Mode Switch does. That's the vintage mono experience, and you can sit anywhere and listen.

A better Mono Cartridge? I found a AT33PTG/II Mono Cartridge with a broken stylus. I had VAS Audio put a line contact on boron on it. That's what is on my left arm now, my Grado a spare, and to bring to friends homes.

c. Modern Mono: my friend (met him here) brought his collection of Beatles Mono and Stereo Versions, we played both versions, with their proper cartridges. 

Both of us felt: Mono, the music was good, however we were more involved with the words, the meanings of the songs; whereas the Stereo versions, we were more involved with the sound, took our attention away from the words/stories. Of course it's hard to define when listening to songs we were so familiar with.

Note: if you go for two tonearms, you need a way to select which arm. I have a SUT with 3 inputs, front selectable, and PASS for MM, so only 1 set of cables to my Preamp.