I love this device! Here are the features that matter to me: - It has a powerful 3.3V regulator (500mA), so even power-hungry peripherials (like a microSD) have enough juice. - While it doesn't expose all the xmega's pins (there's too many of those), it breaks out the interesting ones - the ones that connect to xmega's modules, e.g. serial, I2C, SPI, JTAG, DAC. - atxmega128a3u is a powerful chip (compared to AVR8 chips that are usually used in AVR devices like Arduino): it runs fast (32MHz), big flash space (128kB), lots of USB endpoints (so one can have many USB "devices" at the same time), crypto module (AES128 is fast), digital-to-analog converter (so that one doesn't have to fiddle with PWM). The disadvantage is that it's XMEGA architecture, so one needs to use avr-gcc directly and there's less libraries compared to AVR8/Arduino. - Stephan's MassStorage bootloader is great! Very easy to upload new firmware, and exposes functions for writing to the flash/firmware space from the firmware itself (see "apipage" example on AVR stick's webpage). - Stephan is very helpful when contacted.