tom......
A little more information would be helpful, starting with the machine used to create the files. There was a period in which Zip drives created the 'click of death.' Without being able to test the proposed Zip drive, you could well be buying a defective drive. While the chances are slim, they still exist and that chance could destroy your files, or at least, distroy easy access to them. You can always pay big bucks to have the files professionally transferred.
We bought our first zip drive in the mid-ninties. We soon bought two more because they were so useful. Then, three or four years later and a couple more drives later, I believe before Y2K - remember that circus? - we encountered our first click of death. The drive chatters for several minutes trying to mount the disk. Oftimes, that was the last time the disk would work.
Another problem arises as you move a disk back and forth from an older computer to a newer computer and then to an older computer. It had to do with 'rebuilding the desktop' on the drive or disk. If the newer OS automatically rebuilt the desktop, the older OS might have trouble reading the disk. I always said NO to the rebuild request, made a backup copy of the Zip files onto a hard drive, and then rolled the dice to see what would happen.
The safest route is to find a user group somewhere that has a way of testing your disk and proposed drive. At some point, we aquired a SCSI Zip drive that had a white case. That drive has never failed us so it is the benchmark. Second, we have never had the click of death from a USB Zip disk so that is a second hope for success. Bottom line, you are gambling with the files when you do not know the generation of Zip drive you are buying. Good luck.
If you are in or near Washington State, ie Seattle or Spokane, we can guide you to some resources that would help you work out the details. More details about your equipment would help eliminate concerns.
Ji~m
PS, original Zip disks came formatted 49 meg Mac, 49 meg PC so they would mount on either platform. If files were created on a PC, the Mac would read them. PCs would not always read the Mac files. If you are using a USB Drive and not moving from Mac to PC, you should only have to worry about testing a disk on the USB end before testing a disk created in a SCSI drive. The devil is in the details.