I saw the NeoFami and other clones when I was in Japan as well, and I'm willing to bet that they are not official. I didn't see Nintendo's seal anywhere on the box, so that's pretty much a dead giveaway. With that said, if you find one dirt cheap (they're not very expensive anyway) and wish to play old Famicom games, I see no reason why you shouldn't buy one. Me myself, I'm a hardcore gamer, so I only deal with the orginals, like the 1983 Famicom because it's a collector's item. Some people don't care for the original 1983 Famicom because it's RF only, and it's a pain in the arse to get it to work on a US set, so for these people a NeoFami is a better choice.
