How easy is it to loose micro SD cards?

Here is a simple, screw top, micro SD card holder which can hold up to 24 cards.

This is a re-design is inspired from bgill's micro-SD cardholder, adding a circular arranged slots, textured grips on the outside. (16, 20 and 24 slot versions available)

Take care opening, as the microSD cards can tip out. Perhaps it is a good idea to print the top and bottom pieces in different colours so you know which way is up.

Dimensions: 50mm diameter x 21mm

Edit: 29 May 2017
Added second lid with different grip to help differentiate top and bottom.