Owned two of his headphones and one of his phono cartridges. His greatest advancements were in his early days. His SR200 headphones were cool when I first got them, but hey would hurt my ears after a while. Switched over to AKG K601 and they both sounded better and were far more comfortable. Changed out a Grado Signature MR8 for a Denon DL160 cartridge, and it was also a noticeably superior cartridge without the "Grado dance" on warped records.
Joseph made a lot of advancements in his early days. Those were mostly before I got into high end audio, so I have no knowledge how they compared to others. He tended to do things a different way than most others. With the advent of high output moving coil cartridges, I think the need for the moving iron Grado cartridge fell away. My Denon DL160 tracked records that my Grado cartridge could not and only slightly distorted on the most extreme tracks of my Shure test records.
Still, the guy was an Icon and we have lost most of the early Post WWII audio pioneers.