This review was originally published in December 2014.

Many Mac owners also own an iPad and a new app allows using the tablet as a second monitor for the Mac. Two monitor setups are generally more productive than those with only one screen. A new app for iOS allows the iPad to function as a second monitor for the Mac.

Using an iPad as a second monitor for Macs is nothing new. Apps have existed for a while that make this possible. Where these apps have fallen short is by using Wi-Fi to connect the iPad to the Mac. This works well enough sometimes but the wireless connection to the iPad produces laggy performance. It's not a killer but it is annoying.

Duet Display, produced by former Apple engineers, deals with the lag problem in a unique way. The iPad is connected to the Mac with a standard charging cable for the iPad. This can be either the current Lightning cable or the 30-pin version for older iPads and iPhones.

The app is $14.99 and once installed directs you to download the free Mac app to enable the connection. The iPad instantly turns into a second monitor and is recognized by OS X on the Mac just like any external display.

You can customize how the iPad is used as a monitor through the Displays setting in OS X. You can drag the arrangement of the two monitors to match the physical arrangement of the two devices.

The Duet Display people claim that the wired connection makes the operation of the iPad lag-free. In testing this is largely true, although lags were sometimes seen while playing YouTube video on the iPad. To be fair, the lags were only in the beginning of the video and they disappeared after a short time.

I have been using Duet Display to connect my iPad Air to an 11-inch MacBook Air. The small display of the MacBook Air benefits greatly by having a second monitor. The iPad Air works in full Retina Display format, something the MacBook Air lacks. Touch control on the iPad works as usual, and provides a unique method of interacting with OS X which lacks onscreen touch.

One of only two settings in Duet Display allows switching off Retina Display functionality. The app indicates that using the higher resolution hits the battery harder. Turning it off might be preferable when using Duet Display with a MacBook on battery power.

The second setting in the app also deals with battery life. The frame rate can be toggled between 60 and 30 fps. The lower performance setting results in using less battery than 60 fps.

Having long used Air Display, a popular app that uses a wireless connection between the Mac and iPad, I can attest to how much better the wired connection is with Duet Display. Video response is so smooth and fast you forget you're not using a 'real' monitor. While a physical connection is a little more trouble than wireless, the benefits are well worth it.

Duet Display is $14.99 and the Mac app is free. It works with any iPad running iOS 6 or later, and on Macs running OS X 10.9 and up. It will also work on iPhones, but it's hard to imagine that to be of much benefit.

The Duet Display solution is the first good enough for the enterprise. Companies with Macs and iPads in use can have the benefits of dual monitor setups with just the $15 app and a $10 Lightning cable.

Pros:

Seamless performance

Adds touch control to the Mac

Fully OS X compatible

Cons:

Requires a wired connection

Can't charge iPad while connected

Reviewer's rating: 9.0 out of 10

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