It's a nice design. Simple and functional!
I made a customizable version of this (there is still a link to your original design though). see http://www.thingiverse.com/thing:1751792 I wanted to show you what you can do in customizer :-) Because these types of things are ideal for it in my opinion. I also added a label and rounded the edges because they might be a little sharp when carrying around.
I am using an ultimaker by the way. If you have any further questions please send me a private message :-)