I have been using Iomega Jaz drives (3 of them) for several years. I do not think that these drives are suitable for "mission critical" work. I have now lost the contents of three separate cartridges. These cartridges fail, without warning. When you try to access them (on any drive), the cartridge goes into a clicking mode and can't be read.
I now believe that the cartridges just wear out. I think it is particularly inadvisable to leave the cartridge in the drive, as with every boot of ones computer, the drive is accessed and spins up the cartridge. perhaps it would be safe to keep the cartridges in a desk drawer, and just use them for a minute every month or so.
I have had better luck with 100 meg zip disks, but again, they have this tendency to fail without warning. 250 meg zip drives have, in my limited experience (I own 5 of them), slower than 250 meg drives. Because the 100 meg drives will not read the 250 meg disks, one loses the benefit of nearly universal accessibility if one uses 250 meg disks. All in all, at this writing, purchases of 250 meg drives is an iffy proposition. Purchases of 250 meg disks seems to me to be an even worse idea.
The tools available on the web that concern bad Jaz and Zip disks (such as Steve Gibson's click of death checker), are good for education, but can't repair bad Jaz disks. What seems to happen is when the program hits the bad sector (?), everything stops -- it might finish in a century or two.
To summarize, in my experience, Jaz disks are insuitable for work where it really matters if your data remains intact. There is no method to keep them from failing or to repair them after they break. Of course, this is only my own experience, and I cannot speak for others.
TCH