I had one of these as well as a handful of iButtons. I think I still have them in my box of "maybe this will be useful some day" electronic junk that will never be useful. I got them, as well as some iButton readers of different shapes and sizes, as free samples from Dallas Semiconductor back in 1999 just because I thought they were neat. Never found a use for them, but it was fun to have a "class ring"-size ring that contained some favorite bookmarks.

I have only seen iButton's "in the wild" in one use case - for tracking the nightly rounds of security guards in commercial buildings/industrial complexes. You've probably seem small round discs on the wall in office buildings (normally a round disc with a concentric ring); those are iButton terminals. The guards each have a keychain with an iButton, and as they do their rounds they press it on the terminal to record proof that they went to each terminal at the proper time. Obviously this is a use-case for NFC or a variety of other technologies but for some reason I've seen the iButton-based systems used in a half dozen buildings.