They would likely perform worse. If ("if", ha) those fans are not in perfect sync, they're going to obstruct airflow. Also, consider that each fan introduces both audible noise and perturbations in the airflow which in turn, also will cause noise.
Incidentally, I have (almost) that very same case, an Antec P182. Mine has a super-quiet PSU fan, and a ginormous heat pipe cpu cooler (HR-1 if you're curious) with one fan ... and that is plenty.
But keep in mind that the sound of the cooling will be irrelevant once that user starts typing, as their mechanical keyboard will produce enough sound to not only drown out the fans, but also to shatter their eardrums
Putting a fan after another will up pressure (doubling in theory), but not displace more air. Except if the air has to go through something slowing it down where more pressure will help to push more air through it.
There are obviously lots of variables at play (the extra fan takes up space too, reducing airflow for example) so you are surely right that it's probably useless or worse to have a "double fan" for a PC cooling system, but the fans being in perfect sync is just a noise problem (on small fans like this).
Forget about jet engines. This thing probably sounds more like a helicopter at close range! The ironic part of this is that it could actually lead to power supply issues, which can be just as bad...
Luckily you can get this fractal case with sound damping side panels! It probably sounds like a helicopter in a subway tunnel below you with the panels on.
For shits amd giggles, I put a couple of industrial 10W fans in my PC once. That probably still made more noise than this. It also created so much overpressure that I could feel air escaping the tower from every little hole or crack. You could hold a piece of paper to the side of the pc, and see it moving because of the air escaping between the side panel and the main hull.
But if these are normal fans (max maybe 1,5W), then the amount of power drawn will be the same as a couple of hardrives.
i genuinely have a pc with a 30 cm fan from a welder bolted to a hole in the side of the case, it runs at 240v and it's one of the loudest things i own, but at least i passed from being continuously thermal throttling to running at a reasonable temperature...