Suitable product for internal SCSI zip drive
The description of the product on this site is in accordance with what is noted on the packaging of the adapter: it is possible to put a 3.5" hard disk in it but the aesthetics of the tower will take a hit because the adapter is not completely closed and cannot be, the opening on its front will let the hard disk show through.
I have installed an internal SCSI zip drive without any problem. You will need to have some screws to install the 3.5" hardware in the adapter, as it only comes with 4 screws to fix it in the 5.25" tower bay. The zip drive is screwed in from below.
To conclude, good product with a correct plastic. However, the description on this site should be completed by specifying that 3.5" equipment other than a hard disk can be installed.