Last week, a leak from YouTube channel Tech Buff PH showed off Xiaomi’s upcoming Mi 11 Ultra. Other specs aside, the phone’s most intriguing aspect was a second screen on the back. This screen should be helpful when you’re taking photos with the rear camera, and might even show notifications. That got us thinking: the concept of having a second screen on a phone is not new. In fact, we’ve seen a bunch of brands take a swing at dual-display devices over the years, with varying degrees of success. Let’s take a closer look at the form factors that have…

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