Your post is commercial, but that's okay.
I took a look at your shop and I like the things you developed.
I also like your tests with magnetometers:
http://www.pitlab.com/autopitlot-articles/comparision-of-magnetometers.html
Most common Arduino boards use 5V, and some use 3.3V. Also the 5V boards have often a 3.3V output pin for sensors.
The I2C bus can therefor be a 5V I2C bus or a 3.3V I2C bus.
In many situations a 3.3V sensor can be connected to a 5V Arduino board with pullup resistors to 3.3V.
If you want to provide information for Arduino users, you should tell how to connect with 5V or 3.3V.