This adapter does wonders, that is if you want to play American N64 games on a Japanese console or vice versa. What this basicly does is bypass a couple of tabs at the bottom of the cartridge slot in the N64 console.
The adapter itself does nothing more than that, there's nothing inside the adapter that does any tricks as the Japanese and American N64 carts use the same lockout chips.
Another way to bypass the "tab" lockout is to open up the N64 console and remove the piece of plastic with the tabs attached, so no need for a pricy adapter.
The adapter does look cool though when it's attached to an N64 cart :-)