I think that one huge mistake that people often make is spending a lot of time going through "This is how you create a contact", and then entering in fake field

I think that one huge mistake that people often make is spending a lot of time going through "This is how you create a contact", and then entering in fake field data into forms. And you can edit that form, and then go edit and re-save the data. And often that data is gibberish anyway. Unless filling in this magical form is part of the core value prop, it's really boring, and most people know how to fill out a form already. A good demo should get to the meat of the problem, demonstrating the value prop very quickly. If you really do add value, questions will come up around the "whole product". But if you start with the "whole product" you could lose them before you got to the really interesting parts. Later, if people ask you mundane questions, "How do I change the create a contact, or edit it", you can go back and show that just to satisfy them that it really is just that easy, and that they could do it.