Army may know how to design great looking mezuzah cases but they don’t come in sizes that make sense based on the actual sizes that mezuzah come in.
In the picture you can see how a normal 10 cm mezuzah is just a drop too big for the case and yet it is way bigger than it needs to be for a 7 cm mezuzah which is the next size down.
My recommendation is to always buy cases that fit at least a 10 cm mezuzah klaf. 7 cm klafim are too hard to find even if you are willing to spend top dollar. Better yet, stick with 12 cm and 15 cm klafim as most of the nice mezuzos are written in those sizes.