If you're going to spend $50 to $70 on a phone-charging cable, it had better do more than just charge your phone. The pricey Meem does: As it replenishes your device’s battery, it also backs up files without using a cloud service. That way, when you get a new phone, you just shuttle your photos, contacts, and text messages from the neon-green cable to your new device.1

There's a pretty clear indication that Meem is more than a basic phone charger. Right by the Micro USB or Lightning connector that plugs into your phone you'll find what looks like a thumbdrive grafted onto the cable. And that's pretty much what it is. The extra $20 you spend on the iPhone version of the cable gets you twice the storage: The Android version of the cable offers a disappointing 16 GBs of space, while the iPhone cable has 32 GBs.

When you plug Meem into your phone for the first time, the phone prompts you to download the Meem app. It’s free, and once installed, you set up a four-digit PIN for accessing data on the cable. The app then guides you through the Meem's cleverly designed UI. Managing backups is done via taps and swipes, an abstract and confusing process until you get the hang of it. If you need a refresher, you can tap on the app’s background to read the guide again.

With the app launched and the phone plugged in, the left half of the screen represents your phone’s local storage. It lists categories rather than files: Meem’s data-handling powers are limited to pictures, videos, tunes, text messages, contacts, and your calendar. You don’t have the ability to select individual files for backup; Meem simply copies everything that fits those descriptions.

The right half of the screen represents what’s copied over to the Meem. To manually start a backup, you drag your phone’s icon from the left side of the screen to the right. You can deselect data categories by tapping on them in the Meem half of the screen: Tapping “Photos,” for example, will gray the word out and omit pictures from the current backup. The cable also creates iterative auto-backups every time you plug it in.

There are rudimentary monitoring tools built into the interface. Swiping down from the top of the screen shows you how much time is left until the backup is complete. Tapping the middle of the screen shows how much storage space is left on the Meem. It would be nice to have more-granular controls—a list of files and some plain-English drop-down menus—but Meem does its job of being fairly straight-forward and simple.

Your first backup will take a while, so it’s best to do it while charging overnight. Meem isn’t fast: It has a data-transfer speed of a gig every six minutes, so a 16-gig load takes more than an hour and a half. It appears to back up files in chronological order, so the last videos you shot may not make it to the Meem if its capacity fills up. Once the initial heavy lifting has been done, it gets much quicker: The system just adds new files on subsequent backups.

When it comes to putting all your stuff on a new phone, it works the same way. Plugging in Meem prompts you to download the app and enter your PIN. Once you do, you can start the loading process by dragging the Meem icon to the phone icon. It takes just as long to load stuff as it does to back it up, and you can omit certain types of files by tapping on the category to gray it out. That's as granular as it gets. To read your archive of text messages—one of the unique features of the phone—you'll need to accept Meem as a separate messaging client. Once the transfer is complete, however, you just switch back to you normal text client and all your messages will be there.

Meem is useful, but it has shortcomings beyond its limited storage space and slow speeds. The big one is that it can’t handle cross-platform data transfers: If you buy the Android version of the cable, it can only put your data on another Android phone. Same deal with the iPhone cable. And while it's nice to have PIN-protection for your files on the cable, a four-digit code is pretty bare-bones. If someone gets ahold of your Meem cable, it'll probably be easier to crack that four-digit code than your phone's lockscreen.

The biggest shortcoming for me is that while the Meem module may look like a thumbdrive, it lacks the same plug-and-play capabilities with a computer. It doesn’t let you dump your phone backup to a PC or external drive, although Meem says it's exploring ways to do that. Still, Meem does exactly what it says it does—albeit slowly at first, and with limited management tools. If you want a cloud-free way to keep your phone's photos, contacts, and music, this is a clever and easy way to do it.

1UPDATE 7/27/2016 10:00AM ET: An earlier version of this story listed Meem's prices on Amazon. The cable costs less on Meem's website.