Looks like a Starwars stuff or a battle ship to me, this SEGA MEGA DISK. I am pretty much sure that this thing is not a licensed SEGA Peripheral. The manufacturer is Sane Ting Co. as its indicated at the bottom part.
Basically this stuff is used to,in a good word "copy" ROM Games to floppy disks or floppy disk write games to empty floppy disks, and of course you can use it to play those copied games via floppy disk.In short, produces repro's , copies or whatever you may call it. ER , I don't even want to talk about PIRACY =/
I Have seen stuff like it before but this particular model seems to fit MODEL 1 units because of its circular hole shape at the bottom.
The thing is huge and bulky so it covers almost 80% of the Megadrive when you place it for use.
The cartridge port is located at the right top part of the unit.
The machine is working when i plugged it. The screen showed that it is indeed booting but, i don't have floppy disks with me yet to try and write some games.
I don't really think floppy disks are that reliable though specially when it comes to durability. Of course , unlike your game cartridges that can last really long and withstand impact, heat and etc, i think floppy drives are very sensitive. "FLOP"? but, definitely way way cheaper than the original cartridges.