How would you say your board competes with, or differentiates from, the Teensy3?
As others have mentioned, one benefit of the Neutrino over the Teensy is that you never have to pay royalties.
It's ironic, but if the Teensy had been truly open hardware I'd never have bothered designing the Neutrino in the first place. A year and a half ago I was looking at upgrading some of my existing designs and the Teensy 3.1 was the first board I looked at. I immediately fell in love with it, but the $8 price tag for the mini54tan chip, which couldn't be more aptly named, was too steep, and I didn't want to give up all the Arduino libraries I'd come to rely upon.
And speaking of libraries, another benefit is all the libraries that will be written for the Zero will be compatible with the Neutrino; even if they do direct port manipulation for increased speed.
Finally, the Neutrino features an OR controller which allows you to seamlessly switch from USB to battery power, while the Teensy requires you to cut a jumper to separate the USB supply from VIN.
When using the Teensy I found it annoying to have to cut that jumper on every board that I would be powering from a battery to prevent the battery from being damaged, and once I'd cut that jumper I found it annoying that to conserve battery life I had to keep flipping the power switch on and off as I debugged my program. With the Neutrino, when you're connected to USB the board is powered from the USB. When you disconnect the USB, the battery takes over again.
OP, this is a very nice board with plenty of ROM and RAM. What bootloader do you use to make it compatible with the Arduino IDE?
The board uses the Arduino.cc Zero bootloader and appears as a Zero in the IDE.