Oh my, that is excessive!

I don't recall ever hearing such system in my country, so I expect this is a US-only thing (I'm from Europe). I don't think this kind of system would even be legal in my country, nor would it be socially accepted.

Semi-trucks work just fine with regular silent brakes in the rest of the world, so is there any legit reason to equip a truck with such system, apart from the driver thinking it is cool?

Holy moly, those american style haulers seem to be designed specifically to produce maximum noise? EU trucks and buses have similar kind of exhaust brake that hardly makes any noise