I have oily skin so trust me when I tell you I am always on the lookout for products that will take away oil. This is a new product from NYX, I've only used it once but here are my impressions thus far:
The consistency of the product is hard to describe. Imagine a gel that doesn't feel gooey, more like a velvety texture (somehow that makes sense). Once you spread it on your skin it disappears instantly so I feel like I need to squeeze more product out (but less is probably more). This product doesn't do that weird thing that some primers do, I think it's called pilling, when there's like little balls of the product that don't blend into the skin (just in case you were wondering...).
As far as the mattifying purposes I do feel as though it made a difference in the oiliness on my face, especially the T-zone area. It's not a miracle product, you still need to powder, but I really do feel like it made a difference. I got through most of the day with no shininess whatsoever.
I put it on after my moisturizer and primer, before foundation. It's a little pricey for NYX, @ $13, but I think the price is justified as there are relatively few "low-end" products that are similar. Urban Decay makes a very similar product for twice the price. I also really like the packaging, sleek, easy to use, and air plane friendly.