When two former Apple engineers pitched me a portable, battery-operated blender for my existing bottles — one that now counts Apple design legend Jony Ive himself as an outspoken investor — I saw it as a curiosity. Who’s going to spend $129 and lug around 1.5 pounds of batteries for a weakly blended smoothie?

But I got one thing wrong about the Cruz BlenderCap: the smoothies aren’t weak at all. There are many other reasons why it’s a niche product, but delicious drinks aren’t one. 

Over the past few months, I’ve crushed fully frozen fruit, pulverized strawberry and chocolate ice cream into decent shakes with the USB-C blender, and wowed my kids with (small amounts) of fresh snow from our refrigerator ice cubes. I’ve consistently had enough battery for six or seven small drinks on a charge, and the included double-wall vacuum bottle kept a smoothie pleasantly chilled for two hours in a car left out in the sun. 

I could see the right person being pretty happy with one.  

Portable blenders aren’t hard to find. I was bombarded with BlendJet ads for months. My father-in-law brought home a $20 knockoff one afternoon, presumably after dodging Bullets and Ninjas at our local big box store.

But unlike most portable blenders, the BlenderCap doesn’t have its own proprietary container. It’s designed to screw onto many of the most popular wide-mouth bottles, including those from Hydro Flask, Yeti, Nalgene, and Takeya, though it also comes with its own vacuum insulated 18/8 stainless steel bottle in the box. 

And it boasts power. The cap contains nine lithium-ion batteries that hold 30 watt-hours of electricity (roughly as much as an iPad) and can provide 500 watts of peak power, or 300 watts sustained. It’s protected so you don’t cut yourself, with three safety switches that need to be pressed down by your bottle simultaneously — so the button does nothing when the blades are exposed. The motor spins up to 18,000RPM, and Cruz co-founder Matthew Moore says it’s overengineered, so you can shake the heck out of it while it does the job. 

Which is good because the downside of blending in a bottle is that frozen fruit, ice cubes, and other solids can’t always naturally reach the blades at the bottom. Even shaken, I’ll typically have a few chunks of frozen peach left in my otherwise well-blended smoothie, but a little vigorous shaking reduces the time the blender needs to run. 

Making a drink isn’t quite as straightforward as I imagined. It took me a bunch of trial and error to figure out the right prep. First, you insert the included collapsible silicone funnel to protect the bottle’s threads from getting sticky, then — if you’re like me — it takes a few unscrewings and re-screwings of the cap to find the right ratio of solid, liquid, and air the first few times you make any given drink.

Like other blenders, you need to add just enough liquid to make frozen drinks smooth, but the limited space inside the bottle means you also can’t add too much — if the bottle’s more than two-thirds full, it’s tough for the BlenderCap to do its job. Too much air can also be a problem if you’re trying for a nice thick milkshake: the blender’s powerful blades can fling ice cream clods to the ceiling of the bottle, where they can clump up and get stuck. 

You also can’t just turn on the BlenderCap and let it do its thing. You can tap the button to pulse or double-tap to blend for 10 seconds at a time, but I often needed lots of 10-second cycles to get a good smoothie or shake. 

For example, a big chocolate milkshake that used two-thirds of a pint of Häagen-Dazs took two full minutes to blend, making the BlenderCap’s minimalist aluminum frame pretty warm. (The instructions suggest you shouldn’t run it for more than a minute at a time, but let’s just ignore that, shall we?)

In practice, I mostly got used to all this after my first week — and I learned to use my ears. When I hear a rough, grindy whirring of blades that gradually gets smoother and smoother, I know the ratio is correct. Too grindy, and you need more water/juice/milk to thin it out; too speedy, and there’s not enough fruit in there. 

My kids’ 14-ounce Takeya bottles turned out to be the perfect size for a small breakfast smoothie or dessert shake, starting with fruit or ice cream and adding roughly a fingertip’s less liquid than it takes to cover the top. I managed to get seven small drinks a week that way before needing to recharge. Unfortunately, you can’t blend while you charge — and at just 12W USB-C charging, it can take 20 minutes before it’s got enough gas in the tank to blend once more.

For me, the hardest part was just figuring out when I’d realistically use a BlenderCap instead of, say, my cheap countertop blender with its wired cord. 

Sure, you can leave the BlenderCap on your bottle when you leave the house and have a fresh blended smoothie at your destination. Milkshake in the park! But it’s a little heavy and can be messy to open, and you may want to carry around the included separate caps for the bottle and the blender (which do neatly screw together) if you don’t plan to drink your drink all at once.

Or, you can blend at home, then swap the BlenderCap for the tightly sealing drinking cap before you leave the house. But that way, the only things you gain over a normal blender are no pitcher to clean and less potential mess when you pour. I do really like the two-stage cap, which lets you unscrew the top to reveal a drinking spout or the middle for a wide-mouth pour.

Me, the only way I could justify buying a BlenderCap is for a workout smoothie or protein shake at the gym. That feels like the perfect fit: no more temptation to buy the gym’s own pricy drinks or trek to Jamba Juice afterward, and no hauling around a top-heavy bottle while I run or jog.

Just toss it in the gym bag, and an hour later — based on my tests — even those frozen peach chunks will have softened enough for a perfect chilly blend. 

Photography by Sean Hollister / The Verge