I use one more like this:

https://www.amazon.com/Exhaust-Cooling-Motorhome-Ventilation-Caravan/dp/B0899KTK16/

It sits barely taller than the stock roof rack; you can only see it from the front or sides with a height or tilt advantage. If you're hitting parking garage rooves with it, you were only an enthusiastic throttle event away from hitting without anything up there. It being round really helps it shrug off branches and such too.

It has actually been quite key to allowing me to still use parking garages after lifting my van and bumping up in tire size. I've been in one where a MaxxAir would definitely have hit.

As for stealth, I think a low-profile roof vent stands out much less than any clearly-aftermarket rectangular addition to the side, but stealth in the context of vandwelling is much, much more about activity than appearance anyway. I do still try to maintain a mostly stock exterior appearance though, because if you can afford to add a bunch of aftermarket gizmos, then you probably have cool portable shit in there too - it's more about reducing attention paid, in my experience. That's why logos are bad, that's why big gangly roof attachments are too, and the same goes for anything on the sides that didn't come with it from the factory.

Main reason to stick with a roof fan is physics, though. Warm air rises and carries the typical things we want to remove with a fan - moisture, vaporized oil, smoke, etc. You need to run considerably more exhaust fan to get the same benefit out of a vertical-mount fan.