Started gravel biking last year, always came back home with either/or mud stripe on back or mysterious little gravel pieces in jersey middle back pocket, this solves (minimizes) the problem and it takes only a few seconds to attach to the seat post.
I tried a couple different brands and this one I liked the best. Simple and secure attachment that doesn't slip off during rides and is plenty big enough to keep things dry with 40s on a gravel bike.