I have the G1 and its stellar! Just make sure you use it on a full frame to get the best experience. The Tokina 11-16 is better for crop, its lighter and has a pinch cap plus its almost undistinguishably just as sharp. That's assuming there is no need for vibration reduction. If I may, a bit of a disgruntled grumble. The G1 will not autofocus on the Z system. It seems to work fine if your fine with manual focus, but my trust has been broken and don't really enjoy using it on the z even though most night shots are done without the aid of autofocus. It was made for a D800 or other big body full frame camera. Fair warning, its a beast of a lens! It sucks to carry around not only because of the weight, but also the lens cap. Its not like a pinch cap. It just slides over the lens petals and magic keeps it from falling off. Mine never has, but that's mostly because I'm super paranoid that it'll drop off unknowingly and damage the front element so I'm constantly checking to make sure its still on.
As for the price, no idea other than I've heard the Nikon is sharper. Curious though that the Canon version has a slot for itty bitty filters near the rear element, whereas the Nikon version has none and you need to invest in a 150mm square filter system, if that's your thing.