From Sega Retro
The MD-Pro set consists of a flash cartridge and a programmer.
The programmer is connected to the PC with a USB and a Parallel cable. However, the file transfers and communication happen through the parallel cable only, as the USB cable is only used to power the programmer.
The cartridge is available in two sizes: 32MBit and 64Mbit. It can hold Sega Mega Drive/Genesis and 32X games.
The software you use to flash files is called DreamWriter and is downloadable at Tototek's website (see external links). It supports not only flashing ROMs to the flash cart, it also lets you flash save files, dump current content of the flash cart, flash games with Game Genie codes, and convert the region of the ROM.
When you flash more than one file, you'll get a selection menu when booting up your Mega Drive/Genesis.