The Aladdin Deck Enhancer is a very rare and coveted peripheral for the Nintendo Entertainment System. Very few were ever made, and thus they are quite prized as collectors' items.
This "enhancer" was (technically speaking) a series of helper chips and memory mappers that allowed people to makes carts cheaper. By keeping the memory mapper chips inside of the deck (or in this case, the deck extension), one could make a PCB of a game, with enhanced sound and graphics, with a ton of memory space, for much cheaper than it would cost to say, assemble a copy of Super Mario Brothers 3, that has a complicated mapper and special chips.
As with all obscure console peripherals, it did not catch on, mostly due to the niche nature of it, and game companies not wanting to rely on people having bought a $100 part for the console.
People felt that the Deck Enhancer was the fundamentally correct design for this original Nintendo system. The idea was expensive deck and cheap carts. This idea came way too late in the NES lifespan to be effective. The company that made it went out of business, unfortunately for those who actually wanted one at the time. For collectors, and lucky Nintendo obsessors, this was a wonderful bonus, since it made the front-mounted unit, and the 10-15 games made or prototyped for that unit greatly valuable.