Let's see what's inside one of them. This one has a cartridge slot along with "many" built-in games.
Single pcb design. LCD is not 4:3 but image does not look stretched.
This black blob is the main CPU+PPU chip, unknown.
Edge connector for cartridge on the back. USB battery charging circuit. Main crystal. And there is 16Mbit CMOS flash where built-in roms are stored. This pcb can accept flash in different packages. 3 color wires are soldered by me, it's for speaker and battery connector, old wires were rusty with failed soldering job.
This is to compare cartridge size with GameBoy cartridge, very small.