It's not "legit" in that its licensed by Nintendo or anything, but since most of Nintendo's patents relating to the NES lapsed between 2003-2005, it is guaranteed to be lawsuit-free. This is the FC Mobile, a handheld gaming system selling for $US40 which plays real NES carts. Like, the ones you have in that dusty box under your old bed at your parent's house. No modding, no dodgy imports (console excepted), no hassle. Oh, except it runs on AA batteries. Guess that's a slight hassle.
FC Mobile Portable NES, Because One Screen Was Once Enough [Gizmodo]