I used to think foundation primer wasn't necessary but now i am a huge believer! It really does help the foundation last longer and acts a barrier between your skin and the make up. My skin is temper-mental, so I used to have pretty messy acne and it still acts up from time to time, but i feel like the primer has helped my skin be safe against the foundation. I have been trying new ones and I'm currently testing out these two: 

So far I feel like my foundation lasts all day with both. But I feel like the Revlon one gives a more matte finish, while the Almay one is more of a dewy look. I do like the way the Almay one looks, I think it look more blended and natural because it's not matte. But I love the look of a matter finish...So I would recommend both!