I've been riding good flapped fenders forever. A billion years ago, good bike shops carried the English made Blummel fenders with their deep front flap. In several years, I'd replace the now tired flap with a mylar one. (Mylar was then popular as film for drafting and I was in engineering school.) Blummels disappeared/got bought and moved over-channel. Deep flaps went away. I'd buy (and still do) fenders and before I put them on, drill out the rivets, remove the toy flaps, make real ones and secure them with SS bolts, washers on both sides of the flap/fenders and either nylocs or lock washers. My flaps come down most of the way to the road and have enough stiffness, curvature and width to stop a lot of water. That front flap does more than all the rest of both fenders.
I ride alone and do not put on rear flaps. They suffer when I wheelie the bike out the garage side door and drop it down the step. (By far the easiest way to get through that narrow door.) If I started riding with someone, I'd have to change.
Edit: to GamblerGORD53 - my flaps don't run quite that low but close.