Emulators themselves are legal. Flash carts are legal. Downloading copyrighted ROMs is not.
However, I can offer a about these multicarts, how they work, and where to legally explore NES games. 400in1 nes rom download full
: On standard $5 handhelds, you generally cannot replace the internal ROM without advanced hardware modification because the chip is not designed to be rewritten. Where to Find Custom-ROM-Sup-Game-Box-400in1/index.markdown at main Emulators themselves are legal