OK...I've ditched my mono cartridge

What are the "very high end stereo" you claim I've compared it to?

I wouldn’t claim that the AT 33MONO is the last word in mono cartridges, but for me the things that it does well with mono LPs outweigh its shortcomings relative to the excellent stereo cartridges playing mono that I’ve compared it to(AT ART7, Ortofon MC2000, Accuphase AC-5, and many vintage MM/MIs.) The 33MONO performance is calmer, more organized, and less of a shrunken bullseye than the stereo cartridges. It has good bass, but perhaps less "sparkle" and "life", as stated by OP. However--particularly on old records--it is much quieter in the groove. IMO that is the raison d’etre of a mono cartridge. Of 6000 or so LPs I’ve collected just 100 monos, from ’50s/’60s jazz through recent audiophile reissues of Miles, Coltrane, and Beatles. At my modest level of commitment to mono, the 33MONO is my fav cartridge and a reasonable value. It doesn’t deserve a drubbing.

OK folks, is there one single component or aspect in this hobby we all can agree on?  None that I can think of.

So both halcro and dgarretson are correct for their own perspectives.

In my view the value in bothering with a dedicated mono cartridge is based on two considerations.  How many mono records do I own?  And are they original mono releases, and therefore produced by mono cutter heads, or are they reissues, say since around 1990 and likely cut with stereo heads?

Then it becomes a question of coil design (vertical pickup or not) and stylus tip design and size.  Horses for courses as they say.

I have a Zero and a higher end Koetsu. Also, an arm that allows a moderately easy change.

The Zero is fine, but it lacks the ultimate refinement of the Koetsu, on EX mono records from the 60's.

I have done quite a bit of research and thinking on this subject.  Before you can dismiss mono cartridges as a class, I think you have to consider how the particular mono cartridge(s) you are evaluating was constructed. Only a few were constructed so as to be unable to respond to vertical motion of the cantilever/stylus.  One example of such are the Miyajima mono cartridges, which were designed to be mono in the first place.  (TSD and Ortofon may also make "true" mono cartridges.) Almost all other mono cartridges are stereo cartridges that have either been modified internally such that the capacity to respond to vertical displacement is reduced (and then the two channels are bridged at the output) or are merely stereo cartridges where the two channels are bridged at the output.  (Art Dudley reviewed 3 mono cartridges in one article wherein he tested each for its capacity to reject noise due to vertical motion of the stylus; the 3 were very different from one another in this capacity.) Obviously these 3 basic approaches can make quite a difference in the degree to which a given mono cartridge can be superior to using the mono switch on one's preamplifier.  This is why, if I buy any mono cartridge, it will probably be a Miyajima, but then I would still use my mono switch.  Unfortunately, the preamp driving one of my two systems lacks any mono switch (Atma-sphere MP1).  I am thinking of replacing the function of its "phase" switch with a "mono" function. Miyajima or no Miyajima, I would use BOTH the mono switch and a mono cartridge, optimally. (Have you tried that, Henry?)

But Henry, you did give the impression that you were comparing the dirt cheap AT mono to some very expensive stereo cartridges, although I don't believe you named them specifically. Meantime, I am quite pleased with the effect of using the mono switch that is available on my second system; it's such a big improvement over playing mono LPs in stereo that I don't play mono LPs on my main (no mono) system any longer.