For those who can't watch (it's fairly short) the big takeaways I get is that the DM can set up encounters ahead of time. There can be hidden monsters and monsters that are in a hold area that can be added later. Another nice feature is that you can save the encounter, which would be handy for me as occasionally I've had to end a session in middle of combat. Initiative and HP can all be tracked, as well as adding a colored border that we used for noting conditions.
They only show things from the DM's side of things. I think the biggest issue for me, either as player or DM, is always going to be using something like this if I don't have enough screen space to have both map and DDB up at the same time. But it seems decent for what it is.