It's bendy so it won't break. It's thin so it's easy to get it on a keyring.  It may even help you get other keys on that keyring!  Useful for keys, flash drives, 2FA devices, or anything else that fits on a key ring.  If printed on a flat build surface, you can get a smooth finish on one side onto which you can write with marker or adhere labels.  By the way, Dymo D1 labels stick VERY WELL to the smooth side of this if it's printed in PETG.

It's recommended to print on a flat build surface, with PETG and when sliced using .2mm layer height you should have 3 layers.  There is no infill, but it still only uses 1.3g of filament for each tag.