The board works fine, but is not a 100% compatible replacement for an Arduino Pro Micro, because the dimensions are different. On a real Arduino Pro Micro the distance between rows of pads is 0.6" (15.24 mm); on this board the distance between rows of pads is 0.7" (17.78 mm), so you cannot install this board on a PCB which was made for an Arduino Pro Micro; this fact is not mentioned in the description. On the positive side, the USB socket looks sturdier than on most other Pro Micro clones (it has through hole retaining pins). The bootloader USB device ID is 1b4f:9207, which corresponds to the SparkFun LilyPad board and is somewhat unusual (some software may not support it).