Users of the latest batch of Analogue's Mega SG are reporting they are unable to jailbreak it using SmokeMonster's custom firmware, despite using different capacities and brands of full size SD card.(myself included)
For the uninitiated, the jailbreak allows the Mega SG to play ROMs from Master System, Game Gear, ColecoVison, and of course the Genesis libraries straight from the SD card slot as opposed to a need for something like an Everdrive (it's an either / or situation, you don't technically need both).
Other methods like downgrading the firmware also don't seem to be working, despite the fact this was usually possible in past revisions.
Analogue themselves has stated there isn't anything significantly different about this batch as compared to previous shipments.