I have owned the ZYX Airy 3, Original UNIverse, and 4D cartridges.
The 4D was actually my favorite of those three.
Now, there may be other reasons for that. The Airy 3 and original UNIverse that I owned had the silver coils, whereas the 4D had the copper coils.
However, the fact that ZYX changed the body design of the UNIverse II to look more like the 4D might also imply that others thought the 4D, which was released about 5 years after the original UNIverse design, may have been a better cartridge design.
The 4D was actually my favorite of those three.
Now, there may be other reasons for that. The Airy 3 and original UNIverse that I owned had the silver coils, whereas the 4D had the copper coils.
However, the fact that ZYX changed the body design of the UNIverse II to look more like the 4D might also imply that others thought the 4D, which was released about 5 years after the original UNIverse design, may have been a better cartridge design.