The Polaroid 300 is the Instax mini. I've got one and it looks exactly like the 300, right down to the little dimple on the shutter release.
Note that Polaroid has marketed Fuji's Instax film before, as the Polaroid Mio. The Mio camera itself was shaped a little differently from Fuji's instax camera. Now all they've done is painted it a different color.
I'm all for it, whatever it is. I think the Instax is a fun camera, and fun film of good quality. Too bad Polaroid doesn't have the marketing punch it once did. Does anyone remember "Meet the Swinger, the Polaroid Swinger". I was probably 5 years old when that campaign ran and I can still sing it.
What kind of catchy jingle can you come up with around the "Polaroid 300"? Nothing, really. "Instax" isn't much better.