AFAIK, the main thing is they were the only tapes the SuperStation drives would officially write to, while being able to read other formats.

The Sony SuperStation External Tape Drive can read / write the SONY SuperStation 10GB and 6.6GB tape cartridges as well as read the QIC-Extra, TRAVAN, QIC-WIDE, and the XL Imation tapes as long as they have been backed up using Seagate Backup Exec.

http://www.activewin.com/reviews/hardware/tap … ion/sss_2.shtml

Sony has a long history of proprietary media formats to lock users into purchasing all their media from them.

One of many, many backup tape formats from the previous century. I don't really know if any can be considered special, as there do not seem to be many backup tape collectors out there.
Ads for tapes and drives on eBay and similar sites are either dirt cheap because no one is buying it, or extremely expensive because the seller hopes someone desperately needs the equipment to restore old data (doubt this actually happens).