In my earlier post, I forgot to mention her madjesty Billi is 13 years old, and has only had buttons to "speak" for a couple of years. In the most recent video, I do believe she's expressing both frustration at having to wait and a desire to go walkies outside, separated by "before". I find it extremely interesting, especially because I cannot read Billi's facial expressions at all.
Also, "mad" (modeled as angry, unhappy, disappointed, etc.) being her favourite "word" is interesting, because it is not a demand or wish (like say "food" is), and only expresses her feelings/state and requires no action from the human. Think about it for a second: why would a cat want its human to know it is mad/angry/unhappy/disappointed?
The doggo channel What About Bunny has two smart sheepadoodle puppies, with Bunny using multiple buttons in close succession to express herself. I do believe it is easier for dogs to learn to use such buttons, as they are much more pack-social-oriented. I was giggling with glee at looking how Bunny interacted with "new" humans (parents of her human) with the buttons..