I've been carrying these carriers for a while and they are the most durable battery containers that I've come across. Short of a gunshot, I can't think of a way to destroy one.
I've tried various solutions; Keep2Go tubes, those transparent plastic battery cases, aluminium pill fobs, etc., and found the Delrin cases to be the best. The Keep2Go tube cracked within a week of getting it, the plastic case ripped itself apart, and aluminium fobs were heavy and uncomfortable.
Also, the fact that you there is a hole on the lid so you can daisy chain them together using something like an A&P keyring means that it's modular, as well. I'm currently carrying 2xCR123A, 2xRCR123A, 1xAA and 1xAAA on an A&P keyring, and when I think that I won't need to carry a particular spare, I just take the case out of the loop. If I need to carry more spares, I just put more on the keyring.
Another good thing is that these are quite light and don't have sharp edges to make carrying uncomfortable.
I wish they had cases that will fit 17670 and 18650, but I can live without 'em.