You can use both primers if you would like but the N28 primer is for more dry, dehydrated skin and the mineral veil is for more normal, combination to oily. If you want, I have done this, you can use both, layering them but I find that the mineral veil takes away the moisture the N28 primer serum puts on your skin, so depending on what you like.
The nice thing about the Hourglass serum duo is that YOU are in control of whether to use one, or both. In my case, during warmer months, I felt the white one was enough. But when it get drier outside, I 'doubled up' and added the 'heavy hitter.' I've also done that when I'm going to a special event, and want my makeup to last all night, but don't feel it's necessary for everyday. Either way, they are truly indulgent serums that feel great.