IMHO in use covers are a great idea that got negated by the realities of manufacturing and hitting a price point. They are not really that effective.
Most I see that are actually used very often are either inproperly closed, incapable of being closed over the big plug caps on commercial cords or simply broken off.
I have in use covers on receptacles where I leave things plugged in all the time like my boat lift but I don't have them on receptacles that will be "attended" use. The old code actually had it right in my opinion. The snap cover does a whole lot better job in keeping water out of a receptacle when it is not in use. They are also not the natural home for wasps that an in use cover is.
The fact remains that outside electrical connections are "wet locations" and that crumby little cover does not change that.
