I assume part of the appeal is much cheaper label supplies than eg Epson?

The appeal is the ability to make decent labels which can withstand almost all indoor use and abuse for a reasonable amount of time.

I generally hand-label my boxes and things with specialized ink, and they hold very well even after a decade.

But if I'm going to label a spice jar or something gonna handled a lot, I use the printer. It's legible, resistant/resilient enough and reprinting things is easy.

I think part of it is that these printers end up offering so much more flexibility than your traditional labeler. Single-font single-line labels are boring, crummy built in excuses for emoji…