The guy is a genius. I've been waiting to order the mouse adaptor for myself and a friend (he's been out of stock for a while).
Now he's got a keyboard adaptor in the works (finished?):
Sum adapter allows you to connect a USB keyboard HID Amiga. It is designed to be mounted inside the enclosure Amiga 1200. The design was based on a 16-bit microcontroller from Microchip.
Sum has an internal USB stack enables the handling of USB HID keyboard type without having to install additional software on the Amiga operating system. Installation boils down to the imposition of the adapter plate on the system motherboard U7 Amiga 1200.
Sum adapter has a "bootloader", unique among other adapters for keyboards, which enables software updates.