Comments: RedBoard vs. Uno
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Good write up, just one nit. The Arduino's choice of a second AVR in place of a FTDI chip has two additonal differences:
The Arduino uses a second AVR and while it can be simply used as a serial converter it does have the programming connector exposed to reprogram it for more complicated uses. It could be made to appear as a USB Keyboard, USB Mouse, MIDI controller, Misc HID Device, Mass Storage, whatever you can imagine and get the binary stuffed into 16KBytes to do. There are even a couple of it's GPIO pins exposed, opening the door to all manner of hare-brained schemes with multi-CPU designs.
The Arduino doesn't have the FTDI chip, something that didn't matter when the RedBoard was designed but since their recent antics with DRM it might matter to some.
On the Arduino, pins 4 and 5 are multiplexed between the analog-to-digital converter (ADC) and the hardware I2C interface. Is this also true for the RedBoard?
When you mention the USB Keyboard, are you saying that you can just use the GPIO pins to flash the RedBoard so your RedBoard can function as a HID device? If this is the case can I still use a UART to update my code without having to reflash the device boot code.
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That being said, the Redboard cannot be used as an HID.
This is actually the ATmega328 doing this. PC4 and PC5 on the ATMega328 are dual function (I2C and ADC). Because the Redboard also uses the ATmega328 this will be the case here as well. Also keep in mind that what Arduino refers to as pins 4 and 5 are the digital pins 4 and 5 which are not the I2C/ADC pins. Those are referred to as A4 and A5. Check out the Graphical Datasheet for the Redboard for more information about the functions of each pin. If you are looking for a board that uses different pins check out an ATmega32U4 based board which has I2C on D2/D3 like the Pro Micro - Graphical Datasheet. You can also check out the SamD21 boards which offer much more power and flexibility although can be trickier to use. The SamD21 Dev board - Graphical Datasheetis a good place to start.
Other differences between the Redboard vs Uno: I did noticed that the RedBoard is slightly bigger due to the manufacturing process. Certain Arduino Uno enclosures will not work with the Redboard due to the narrow tolerances. Also, the LEDs are positioned in a different location on the board compared to the Arduino Uno.