Very simple-looking, but incompatible with Atari (and therefore Mega Drive) from what I've read. Note that the original Spectrum's Kempston and Sinclair Interface 2 interfaces *do* use standard Atari joysticks. Pinout here: http://www.worldofspectrum.org/ZXSpectrum128+3Manual/chapter10.html
Won't work (for hardware, not firmware reasons) from what I can tell.