The goal of this project : 

I was trying todo something w/ SonyEricson LiveView BTmicroDisplay, but it wasn't fit all my needs.

So I decided to design my own micro display.

It needed to be able to display (relatively) big amount of text, a batt. jauge, some notify icons and colored light.

I needed also something that can plug directly into an USB port w/o requiring an USB cable...

The Teensy3.2 offers this capability by exposing 4 USB pads (to be soldered), it has a very-very small form factor,

the other pros w/ Arduino ProMini was the integrated USB-2-UART + bigger Flash & RAM amount.