Well, I’m thinking that I might have lucked out by being able to purchase this item from Amazon. I was actually surprised that it was available to order as it is usually difficult to purchase mod chips and related hardware from commercial retailers in the U.S. Yet, I did actually receive an R4 Gold Pro Revolution.
The cartridge enables a 3DS (and other systems such as the DSi) to run homebrew software. It’s easy to use, though it requires a micro SD card in order to function and some software that must be downloaded from the manufacturer’s website. The cartridge gets around the typical mod restrictions by simply presenting itself as a valid game to the system.
On the DSi I was able to run some Nintendo Entertainment Emulators (NES). The 3DS is capable of running several others including a Super NES emulator.
Overall, I think this is a very cool upgrade for the 3DS.