Hi djglish, if you don't mind soldering 4 wires you might as well
buy an ATmega32U4 (Arduino Leonardo compatible) board for $10
flash it with this software: https://github.com/devonshire/arduino-atari-hid-keyboard (Copyright Kevin Peat 2017)
solder (or otherwise connect) the 5V, GND, RX and TX wires. The reset wire is optional (and does not exist on MegaST/e).
This works well not only for STF/M/E keyboards but also for MegaST/e ones.
This will however not give you joystick or mouse support.
I don't want to sabotage Tynemouth's great product here, but having to wait until EOY sounds a bit harsh