As long as the Mega Drive uses standard 9 pin joystick ports it'll work! Unlike the Sinclair scam of altering the pinouts on the +2/+3 and forcing you to buy 'special' Sinclair Joysticks FFS!!
I might actually pony up and buy one of them Comp Pros having considered that most on ebay are 2nd hand! Wonder if Amigakit will stock them?