The Micro is clearly a small, breadboardable Leonardo. But it is more expensive and while it does break out the SPI pins (both the data/clock lines only wired to the ISP on the Leo and the SS pin which is not broken out on the Leo at all), it is still slightly gimped compared to Adafruits non-Arduino 32U4 dev board, which also features the RXLED and HWB pins broken out. While one might be able to jumper some wires to the two NC pins, I do not think the Arduino label makes the extra price and effort for a full-featured 32U4 dev board worthwhile. Only good for those who cannot bootload it themselves, I guess.