Demos usually take just 30-40 mins, we'll show you and your colleagues some real customer examples, how you can build similar quickly, and answer all your questions. Tell us about your specific requirements, and we'll focus on those features of the system.
Yes it's a good idea. It is best to consider who else will be using the system and which colleagues or stakeholders benefit most from its implementation, and who is the decision maker/ budget holder :).
No, you don't have to download anything to join the demo. You can just click on a link and dial into the conference. Alternatively, if your IT allows you can download the app and the connect via the internet.