oh, we knew it would read formatted HD disks, or format them in HD, but I'm sure many of us have formatted an HD disk as DD in a pinch, and used on legacy machines. I definitely see a higher failure rate doing that, but on at least Mac and Amiga drives, I've also see it work a fair amount.
The 1591 immediately said "bad disk", as opposed to plugging along track by track and then failing when it hit a bad one. It is a newer drive mech in there, it may be "smarter" than 1990s floppy drives.