Compuware Gomez is a popular tool to test website and CDN performance.
For quick demonstration purpose, Firefox and Firebug can be used to show how a webpage is loaded to browser as well as how CDN improves web site performance, as show is this demo:
What if you want to do a quick demo of how CDN improves file download when you are having coffee with your customer? No laptop? No big deal. What you need are three little things:
Gage: Network Speed Test Utility is a FREE iOS app which tests file download speeds on any server. Add the two URLs in Gage and then you can test and compare how fast (in Kbps) and how long (in sec) to download the files from customer origin and CDN.
Here is a quick demo: