Those Sega pads are supposed to work with both buttons, but recent versions of WHDLoad cuts out the second button for most games for some reason, unless you're using a CD32 pad. If you try some games that support 2-button controllers from floppy you'll see the C button on Mega Drive and 2 button on Master System pads work. Also later versions of AmiMasterGear seem to have the same problem, but I used to play Sega games with a Master System pad all the time years ago.
AmigaManiac's adapters also work with Guitar Hero controllers and dance mats for use with Tracker Hero.
