Review on OSOYOO Pro Micro ATmega32U4 Module Board: 5V/16MHz, 2 Row Pin Header, Arduino Compatible – Upgraded Version with ATmega328 Pro Mini Support by Ryan Bennett

Many old reviews say an error when you need to reset the sketch to make the sketch load after power off. I had this problem, but it's easy to fix by flashing an updated bootloader. I bought my 2016 to make a head tracker for Elite Dangerous. It still works fine but I've now repurposed it as a spinner controller in my MAME case. I recently bought 2 more that I plan to use to make button boxes for the DCS. There are bootloaders on the new ones and I didn't have to update them. You may or may not need to update yours. I don't know if they fixed it or if it's random. To flash the bootloader you need a flasher, this cannot be flashed as a sketch from USB. You can use another Pro Micro with the Flasher sketch loaded, or like I did, you can use a Raspberry Pi with the Arduino IDE running to flash it. You can easily check if you have a bad bootloader by uploading the SparkFun Pro Micro Blinkies test sketch. Then unplug it and plug it back in. If the LEDs don't blink or blink slower, you have a bad bootloader.