Okay, I'm a bit of an expert on the subject of Famiclones and other bootleg/clone hardware. No, an SNES clone is absolutely not legal. And furthermore, many Famiclones are still actually in question (
see this article for more info).
And yes, Nintendo does have a history of going after on Famiclone manufacturers, even in recent years. No one is going to get in trouble for owning one, I can guarantee you that. But if you're a company making them, beware. Though they haven't been as vigilant as they have in the past few years, when they do come down, they come down hard.
Anyways, in regards to this particular clone, they're quite nice; definitely one of the better clones on the market. The SNES functionality is pretty much spot-on, accurate to perfection, I'd say. However, like just about every single NES clone on the market, the sound in NES games isn't quite perfect when played on the FC Twin; you'll notice odd-sounding sound effects, and occasionally warped music. And again, like just all NES clones, there are some games that simply won't run on it; specifically, Castlevania III (I don't think any Famiclones play this game), and Dragon Warrior II, and a few others, I believe.
Still, worth it, if you have neither an NES or SNES.