These unofficial handhelds can play original Mega Drive and NES cartridges.
Until now this only was possible with the Sega handheld called Nomad, which is very expensive nowadays. These here have a very low production cost, which looks obvious. You can also plug them to a TV via cinch cable.
Optically close to the Mega Drive (Pocket MD) model is the Pocket Boy FC-360, which play NES cartridges. The screen measures 2.5 inches and it's powered by 3 AAA batteries. How long the display will give light, and how the compability is, is not mentioned. Btw, nice engrish on the box ;-)