Duet Display-use your iPad as a second monitor

I have mentioned in the past how much writing I do for work. When I write I prefer having two monitors. Unfortunately, I only have second monitors at home and work. I prefer writing grants, white-papers, and manuscripts in local coffee shops or, my favorite spot, the public library. Previously, when writing in these alternate locations I had to make due with the 13" screen of my Macbook Air. I had tried two-screen solutions that used my iPad Air as a second monitor--but they had too much lag to be functional. Recently, I discovered a product called Duet Display. Instead of using a wireless connection, Duet uses a Thunderbolt cable to connect my computer and iPad. Duet was easy to set up and there is absolutely no lag. I can now, thanks to Duet, take my dual screen set-up to any location. My only complaint, the app's cost ($15.99). Still, for the problem Duet solves, I've found it well worth the money.