I think I posted earlier that the first time I became aware of MC cartridges was in the mid 70s, when the Supex cartridge came into the US market. The problem was that few of the existing phono stages had sufficient gain. Within no more than a year of the introduction of the Supex, Mark Levinson (and John Curl) introduced the first ML product, the JC1, which was a pre-preamplifier or "head amp". It was a little solid state box that simply added gain to boost the output of the Supex and I suppose other LOMCs that may have already been available. In my memory, living in Connecticut at the time, I had not yet heard or read about any SUT, but I am sure that the Japanese were ahead of us in that department, at that time. ML was just a kid then based in Woodbridge, CT, outside New Haven where I grew up. That’s the way I remember it. The Supex was highly praised by TAS and Harry Pearson. When later I heard one, I thought it was mediocre at best, certainly not as good as my favorite MM and MI cartridges, at that time.
I have never owned a SUT, but I have heard some systems of very high quality that incorporated SUTs, really good ones designed and built by Dave Slagle of EMIA, that were very satisfying. Nothing to criticize there.