Taylor Made or Silver Screens are the two main makers, both seem good. External ones mean no condensation on the inside of the windscreen, but internal ones may be simpler in bad weather, although lots of condensation between screens and windows. We have external, but also built in blinds for windscreen and snap-on side screens, so easy to use either.
I guess they could flap in the wind if not pulled tight before shutting the door on them .
If you have specific ones for your make of van, then no, no flappage, they just fit.