The Mayfly v1.0 boards use a new USB interface chip called the CP2102 instead of the old FT232RL that was found on earlier Mayfly boards. When you first connect it to your computer, your operating system should recognize it and install the necessary drivers. I connected each new Mayfly to 3 different computers (2 PCs and one Mac) before shipping them out, so there shouldn’t be any hardware problems with the board. You’ll also want to make sure the small DIP switches next to the main power switch are both in the ON position, otherwise the CP2102 will not be powered if the bottom switch is off.
I haven’t had to manually install any drivers for the CP2102 on any of the dozens of Windows computers I’ve used CP2102 devices on. But if you’re having trouble with it, you could try manually doing it following the instructions from SiliconLabs for the CP210x: https://www.silabs.com/developers/usb-to-uart-bridge-vcp-drivers