Luckily i make a living doing integrations so i guess its not a set requirement for everyone. (not like i am an amateur at this - i've only been doing theme integrations for almost 14 years and have done thousands of WHMCS Themes)
Sure, its simple to set up a demo but as I am sure people are well aware - its not to hard to view source, copy the css and apply it to your own WHMCS Theme and not pay for it. (Though not sure why a competitor is worried about my demo's?). As for functionality, well its the same functionality as a regular WHMCS Theme - just a different color.
I used to provide live links on my portfolio for people to see the integrations i did 'live' but of course unsavory people would visit those links and 'rip' their designs.