It's a good question. It's definitely not been through years of testing yet but in the past few months me and some friends have had no problems.

All of the parts have a low center of mass with respect to the PCB and are unlikely to catch on anything. Water and/or sweat won't hurt it as long as it's dry when you use it. I've tested it works fine after putting it through a washer and dryer.

However, making your own casing or 3D printing something like this [1] is always best

[1]: https://github.com/conorpp/u2f-zero/blob/master/hardware/cas...