I had two Atwood/Creation awning windows in my Sprinter.
They looked really good from the outside, and did provide ventilation w/o letting in rain or bugs, but:
The mechanism was finicky and not very robust.
The amount of open area is tiny compared to the window size or to sliders.
I had one in the sliding door and never wanted to slam the door shut with the windows open, since it rattled and clattered and was rough on the rinky dink mechanism.
My first one in the door failed on the first trip! Sportsmobile replaced it at no charge, but they did say that sliders although not as OEM looking, do function much better.
You're buying used, so will have the choice of adding OEM or any type of aftermarket.
This time I'm going with factory all around windows w/ flip-out. I will add my own screen system.
Way cheaper, better corrosion protection, just as much ventilation area, and more importantly.......if I end up hating the vehicle and get rid of it I won't have much extra time and money put in.
I will go with one or probably two Fantastic Fans like I had in the Sprinter though.