While there are several apps designed to turn the iPad or iPhone into a secondary display for a Mac, the most popular options use Wi-Fi, which can render them all but unusable at times due to unavoidable lag. A new app from developer and former Apple Engineer Rahul Dewan aims to solve these lag problems with a tethered solution that turns an iOS device into a more reliable secondary display.
Duet Display, which is launching today, is the one of the first apps that transforms the iPad and the iPhone into an extra display for the Mac using a Lightning or 30-pin cable. By sending data over a cable instead of Wi-Fi, Duet Display is able to greatly improve on the lag is typically present when an iOS device is used as a secondary display.
Duet Display offers both a Retina mode and a non-Retina mode, along with options for 30 or 60 frames per second, and it's easy to install and setup, requiring just the Mac app, the iOS app, and a cable to connect the two devices.
The Duet Display app is inarguably an improvement over other options today, but it is not a perfect solution. As detailed in the video walkthrough of the app below, MacRumors experienced some issues when testing the app. On a 2012 Retina MacBook Pro, Duet Display's Retina mode caused a significant amount of cursor lag, rendering the app nearly unusable, and the CPU usage climbed to well over 200 percent.
Non-Retina mode (which is enabled in the app by default) offered a more lag free experience, but the trade off caused the secondary iPad Air 2 display to look fuzzy -- a disappointment given the inherent clarity of the screen on Apple's newest tablet. Non-Retina mode in Duet Display degrades the quality of all Retina displays to a noticeable degree.
According to the developer, performance is better on Macs released in 2013 or later, and users who only want to view one static window may not have any problems. Furthermore, many users may find the utility of a secondary iPad or iPhone display to be enough to outweigh the lack of a Retina experience.
Though the iPad Air 2 and other Retina devices don't look good in non-Retina mode, Duet Display is a great solution for older iPads that people might have little use for. An original iPad or iPad 2 does not have a Retina screen, and will work well with older Macs as secondary displays. iOS 5.1.1 is not yet compatible with Duet Display, but the developer is working on a fix.
Along with the Retina issue, potential buyers should be aware of some other small issues that we ran into. Even in non-Retina mode, on a 2012 Retina MacBook Pro, there was some slight cursor lag, and we also had problems with visual artifacts on some apps. When watching YouTube videos, for example, there were some occasional performance blips.
The developer assures us that he is working on improving Duet Display, and he plans to release iterative updates in the months to come to clear up lingering problems. As he suggests, it's better to have an app that works most of the time with just a few problems rather than one of the existing Wi-Fi solutions that can be almost non-functional.
The Duet website claims that all Macs using OS X 10.9 or later work with the app, as well as all iPads and iPhones, but MacRumors was unable to get the software to work with a 2010 MacBook Air running OS X 10.10.2. According to the developer, the issue was due to the 10.10.2 beta software, which does not work with the app.
Duet Display may not provide the perfect secondary display experience, but in our testing, we found that it was more reliable than current Wi-Fi options, and we believe it's a fantastic way to make good use of older iOS devices.
Duet Display for the Mac can be downloaded from the Duet website for free. The accompanying iOS app can purchased from the App Store for $9.99 for 24 hours, and then the price will go up to $14.99. [Direct Link]
Update 12PM PT: Some of our forum members have not been able to get Duet Display to work on an iPad running iOS 5.1.1, and the developer has asked people who want to use it with an iPad running iOS 5.1.1 to wait for an upcoming update before purchasing.
