Each pump is shaped like a breast and, when placed over your actual breast inside your bra, simply exaggerates your usual bustline. It's not exactly natural-looking, but it is much more discreet than being shirtless with bottles hanging from plastic cones on your chest. Plus, it's much quieter than your average pump.
This was one of the many goals Naomi and her team had in mind when designing the pump. They "wanted to develop a pump that had few parts to put together and that was easy to clean, that would be quiet enough so you could talk on the phone, and a pump that didn't require moms to undress." The company clearly delivered on its goals. With Willow, I've pumped comfortably in restaurants, cars, and even in the middle seat on an airplane without anyone even noticing. If you're looking for further proof, I'm actually pumping in the photo above! I'm not sure I'd actually walk around in public wearing it, but you probably could without anyone knowing what was going on under your shirt.