That video looks more like dry lining. I used an Ames dry lining machine leaving walls like you see in the video. Then I applied ready mix joint cement as a slurry all over the wall as flat as then sponge finish. Next day sand it all down and it was a perfect finish.
But dry lining never took off as plasterers could not take to it so board and skim came in. Plasterer's prefered skimming. I preferred dry lining.
So what you see is the slurry being sprayed onto what is a perfectly flat wall then a day or two later it being sanded down.
You may have some perfectly flat walls you could spray but others may need that bit thicker material. Thats where skimming comes in.
Ask yourself, does most of the walls you skim just need a mm of dry lining material to get flat and smooth. If so go ahead and buy the machine.