I wish I had ordered the press studs with my jacket. The flaps do stay closed when it is zipped but the studs make them a bit more "tidy" and also can take some strain off of the zipper
I got a LC jacket, so it came with studs as standard.
To be honest, I can't imagine the jacket without them. It would feel "messy" to me, to zip the jacket and have a floppy storm flap. The amount of "flop" of course, will be determined by the leather type.