Now that nearly every cosmetic company makes a foundation primer, hardly anyone is asking if they really need one. If you are asking, let me respond with a question: do you want your make-up to stay on all day?
Smashbox cosmetics were originally designed for models, and designed to stay on during a full photo shoot under hot lights. They developed PhotoFinish Primer because their foundation needed touch-ups without it, and the PhotoFinish with Dermaxyl and SPF 15 was designed for "mature" women who want to improve and protect their skin as well as keep their make-up on.
Currently, the PhotoFinish Primers come in rectangular pump-bottles. This is a shame, because the pump can't get the last quarter or so of product out of the bottle. At their prices, users tend to pry the pump top off, and go after that last bit with a cotton swab. It's worth the effort. Once you get it on, you apply the product to cleansed and moisturized skin. Smashbox describes the feel as "silky;" I think it feels oily, and so do others I've asked about it. The oily feel doesn't last long, though. I do have "mature" skin, although I am mainly wrinkle-free. The Dermaxyl is a patented anti-aging complex described by Smashbox as "an advanced skin treatment which helps to reduce the appearance of wrinkles over time." After using this almost daily for a month, I did feel that my skin was softer, smoother, and firmer, but having no way to measure that, it may have been wishful thinking. I like the additional layer of sunscreen atop my regular moisturizer, which also contains a sunscreen. The PhotoFinish Primer with Dermaxyl looks fainly coral in the bottle, but it goes on clear.
The problems with this product that I see are its price ($42); the packaging, although I've been told by Smashbox employees that they are changing it to a better dispersal system; and the slightly oily feel as it goes on. I think that there are less expensive primers that can accomplish the same thing, without the oil. I would only recommend this to women who don't have to consider how much they are spending.