I almost got one of these stringy floppy drives for my Commodore 64, but then my cousin discovered girls and didn't need his 1541 anymore, so I didn't have to buy one. From what I've read since then, I was lucky that I didn't, as they were supposed to be horribly unreliable.
It's interesting how almost all storage media for the last 70 years is either on a long string, a spinning circle, or now a chip.
Concur on 'almost all', but machine readable 2D arrays (in various encodings) on paper or film substrates have never entirely gone away.
Elsewhere in this thread, Paperbak is mentioned, but there are other similar formats invented occasionally, like DataGlyphs: http://fileformats.archiveteam.org/wiki/DataGlyph
I had the "QL" version mentioned on that page, which maybe explains why they worked better for me, despite their reputation.
I still have a bunch in a box, and I tried to read them just a few years ago, and they all still worked! I was amazed.