The idea of a smartphone having two screens of one type or another is an idea that has been around for several years. Earlier examples include the Kyocera Echo, LG DoublePlay, Samsung Continuum, and YotaPhone, all of which (save for YotaPhone) have fallen by the wayside. However, smartphones with dual-screens still exist today in devices like the LG V10 and the Samsung Galaxy Note Edge.
It does feel like dual-screen displays are starting to catch on, but the idea obviously wasn't always so appealing. Earlier smartphones with two screens weren’t exactly practical or inherently useful so much as it was just a “cool” and futuristic idea to have two screens. The Kyocera Echo featuring two full-sized screens with a strange flipping mechanism certainly looked cool, but as a low-end Android when Android still had major performance issues to overcome meant it wasn’t a popular choice among consumers. The LG DoublePlay had a strange design as well with the secondary display in the middle of a physical keyboard, which made for a very cramped design.
YotaPhone, on the other hand, is another example of a unique take on secondary displays. Although it isn't exactly the most popular device, it was successful enough to release a second iteration in the form of YotaPhone 2, which ended up receiving more praise than its first generation.
The only example where a secondary display hasn’t changed all that radically from what we see today is the Samsung Continuum, where the concept feels very similar to what we see in the V10 in the sense that it is a small “ticker” type of display. However, I think the Continuum flopped because it lacked a lot of changes that I think were needed in order to make this type of secondary display work as well as it does now.
Part of the reason why I think the Continuum didn’t do so well is because back in 2010 smartphones were a lot smaller than they are today. Putting in a secondary display took away from the already limited amount of real estate available on a screen, not to mention a 1.8-inch ticker on a device with a 3.4-inch main display seems a little distracting. With the V10, and also with the Galaxy Edge models, the secondary display is much smaller in comparison to the screen size and, in the end, seems to help and serve a better purpose at this point.
I think secondary displays serve enough of a purpose now that it's a convenient feature to include. A phone’s display is one of the biggest reasons that battery life is so abysmal, and by having the entire main display light up to show one small notification seems wasteful. A secondary, smaller display can do the same job with much less battery life consumption. At the same time, there are other ways to cut down on wasted battery life when it comes to notifications. Motorola’s Active Display is a good example of this, and there’s no secondary display needed.
But there are still other good reasons for a phone to feature two screens. LG’s V10 and Samsung’s Galaxy Note Edge offer some convenient solutions with an always present toolbar design. Quick access to contacts, alarms, apps, notifications, and even act as a ruler are just some of the things that these secondary displays can do for you.
Overall, I think that secondary displays have finally found their time to shine. It might not seem like much, but I don't imagine there's much that should be expected out of a secondary display anyway; it's just a convenient way to relay and access information quickly without much energy consumption. Although it seemed a little bizarre at first (what new design or idea doesn’t, though?) I’ve grown fond of the idea of having a two displays. I wouldn’t be surprised if we see more manufacturers come up with ways to incorporate two screens in more smartphones in the next couple of years.