@gregl said: isn't the key difference of the two that one 32u4 has a built in USB controller, whereas the 328p doesn't and relies on an external USB controller (FTDI usually.) That's important, but there are many other differences vs ATMega328p. Offhand, there's an extra 0.5K RAM. Second 16 bit timer (Timer3) instead of 8 bit Timer2; plus high speed 10 bit Timer 4. SPI and TWI on different pin #'s (as seen by Arduino). More ADC pins, and a 10x/200x differential amplifier; different voltage ref (2.56v vs 1.1v). And various changes to interrupts or registers based on these. So some less-used libraries need porting, as well as changes to example code. Not sure how these differences affect the core of MySensors; you might have to try it out. There's a good chance that it would work, or that the changes needed would be minor. The Leonardo is gone from the Arduino.cc product line, but the Micro is still sold so presumably the chip continues to be supported.