The name is a typo (cheaper domain name)! You do pay to get a video, but it's not a demo. To me, a demo is made by someone familiar with the product who knows how to make the product do something impressive. Videos from Usabl are more likely to include moments of confusion that will be useful inputs in deciding how to design the API surface.
So I would still expect you to pay if the dev struggles, unless the dev doesn't do a good job explaining why they are struggling.
See this link for an example with some highlights (1 minute): https://youtu.be/5o71pRZ-aMk