Air Display is Great, but why £12 0n App Store yet free if you download

I have used Air Display for a couple of months now on my Windows Laptop. It lets me use my iPad as an extension on my Windows desktop. Great for keeping files I want to reference as I do my main work on the bigger laptop.

Now I am a besotted Macbook Pro newbie I naturally wanted it on this, especially as I have the smaller 13 inch model.

So off to App Store, and hey, it costs £11.99, I don't remember having to pay for it on Windows.

So I go to Avatron web page and install by downloading direct from Avatron, and hey presto, it is installed for free!

And I am using it right now!