The left side is a wax that you use to fill your eyebrows and shape them. On the right side is a powder that helps set the whole thing. Interestingly, I had chosen the color #3 for the Goof Proof Pencil but that would have been way too dark with the Brow Zings Kit so I went with #2. In fairness to the product, though, my orange is brighter now than when I bought the Goof Proof Pencil so that may be why the color shifted. This is DEFINITELY a benefit of going to Sephora itself to try on things and assess which would work better for you.
The Brow Zings Kit is pricier than the Goof Proof Pencil ($32 and $24, respectively) but I can already tell that the kit will last longer so that's worth it right there.
One thing that I didn't really see while in store were the tools that are included in the kit. The tweezers are really just meh as they are so small. I do have a better pair so I use those instead. But it can be neat to have those in the kit if you're traveling or something. I was disappointed in the brushes when I saw them because they looked so small. Once unfolded, though, they are not so bad at all. The handles are a little thin but that helps with a lighter application so it woks out.
The application is really easy: you sweep some of the waxy color over the eyebrows and give them their shape and then you just apply some of the powder over it to set them. The application of the powder does not seem evident but it does give the eyebrows a little bit of a fuller look.
So I definitely like the product. We'll see how long it lasts. I do think that it will be longer as 1) I won't break any tips and 2) there is quite a bit of product. And, of course, here's a picture of what I look like with it on.