I see Elvie pumps everywhere. My fellow moms rave about it on Instagram. I find it on store shelves frequently. It sounded like the newer, cooler version of the Willow pumps, which I’ve known about since launch.

But when I finally tried the Elvie, I found myself unimpressed with what the $550 pump could do. It’s not the only wearable pump with such a high price tag, but its competition can do tricks that the Elvie just can’t.

Mystery Size

When the Elvie came in the mail, I had an immediate question: What size is it?

It comes with plastic shields that sit on the breast, in two different sizes. But unlike other breast pumps, these shields aren’t labeled with the number of millimeters to check your size. (Check out our guide to shopping for a breast pump to see why it’s important to get the right size.) I checked the box itself, and the instructions, and came up blank. The website says that the box includes 21 millimeters, 24 millimeters, and 28 millimeters, but my box came with only two sizes instead of the promised three.

It wasn’t until I powered up the app and followed the building instructions that I learned there’s a shape on the shield that designates its size—a circle means 21 millimeters, a triangle means 24, and a square means 28. The app then guided me through checking my size. If I needed a different size than the ones included, I would need to purchase one of Elvie’s cushions to create a smaller size.

If you buy Elvie on its website, underneath the initial product banner it encourages you to check your size. But it’s easy to just click “Add To Cart” above that banner and miss the explanation on sizing entirely. Third-party retailers don’t mention it at all.

These sizes are the average best size for most folks, but not everyone. I don’t use an average-size flange and the difference is obvious when I wear my correct size. Sure, I can still pump with a 24-mm flange, but when I switch to a 21- or 19-mm size, the results are clearly better. It’s frustrating that Elvie doesn’t make it possible to buy the right-size flange right from the start, especially considering the high price tag.

Semi-Smart

Photograph: Elvie

Similar to the Willow 3.0 (7/10, WIRED Review), the Elvie will track in the app how much milk you’ve pumped during a session. But unlike the Willow, I found the readings to be wildly wrong nearly every time.

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