Well if you look at the parts list, you are spending 30-40 dollars for one adaptor. Like I said, if you buy the usb retropad and the snes version, you can actually wire a nes plug to it and have a dual adaptor. Mind you this one is wireless, but that's essentially useless as it's a fixed frequency and thus only one controller can be used. Plus it may be wireless, but you have that big fugly dongle hanging off your wii and you have to hack up your original controllers.
Don't get me wrong, the end result is bad-ass, but it isn't exactly cost or time effective.