Most of the time, I work at the Windows 7 computer in my home office with a dual-monitor setup. A lot of non-geeks have never used a dual-monitor setup: you will just have to trust me when I tell you that, for a programmer or any other person who needs to look at a lot of information all at once, it is much more productive than a single-monitor setup. It's not a luxury—it's a necessity.
When I have to leave the home office and go into the office office, I take a Windows laptop. This is less productive, due both to the small screen size and the fact that I have only one screen. So I decided to try out a couple of apps that allow one to use an iPad as a second monitor. I tried Air Display and MaxiVista. Both apps have been available for a while, but Air Display originally only supported Mac, while MaxiVista only supported Windows, so there was no choice to be made. However, Air Display now supports both Mac and Windows, so I wanted to try both apps to see which provided the better experience on Windows.
Both apps require a wi-fi connection between iPad and computer Both apps require that you download a free program to install and run on the computer side. Both apps are currently selling for $9.99 in the App Store.
MaxiVista was the first app I tried. Setup on my Windows 7 laptop was easy, and It Just Worked. I started the app on the iPad, then started the app on the laptop, and the laptop immediately found the iPad on the wi-fi network. I was a little disappointed with the speed of display updates on the iPad monitor, but it was usable.
Then I tried Air Display. The setup was a little more difficult. After installing the Air Display application on the laptop and rebooting, it started automatically but could not locate my iPad. After trying a few troubleshooting measures, I eventually figured out that it had to be Run as Administrator. After I worked that out, it ran fine.
Air Display provides a better display experience. While MaxiVista feels like running VNC over an Internet connection, Air Display feels like running with a directly connected monitor on a ten-year-old computer.
Air Display lets you use the touchscreen like a mouse. MaxiVista doesn't have that feature (but they say it is coming).
The fact that Air Display works on both Windows and Macs is nice. The "Windows laptop" I've been talking about is actually a MacBook Pro with Boot Camp, so it's nice to be able to use the iPad as a second monitor with whichever OS I have running.
So, to sum up, Air Display is the clear winner for me. It's faster and more capable, for the same price. Even if MaxiVista was free, I'd gladly pay the ten bucks for Air Display.
Update: Note that someone from MaxiVista has responded with a comment describing configuration settings that could improve its performance. (I haven't tried them myself.)