I've watched the video and a few others too and am more than happy that I do NOT use a harness, cloth cage/carrier etc. My dogs usually travel on the floor, either between the cab seats or in the dog bed which is pushed right up against the centre console, the trouble with harnesses etc is that people think they provide a safe way to allow dogs to travel on seats etc and clearly they are not.
This one shows what happens to harnesses ...
Certainly up against a bulkhead or chair/console is good, a harness helps to put/kerp them there. . Personally, having seen seen a dog barking at where its legs used to be after a car crash I couldn’t have mine loose in the vehicle. Sorry for the downer …