Cats will check out every large natural dirt hole they come across in their hunting. Tracks in the snow have let me see this. So if you want to make a big showy dirt hole they are great visual attractors. BUT, in many many excellent cat locations out west, dirt holes are impossible to make. And who wants to pack a heavy digging hammer, sifters etc to the cliffs and rimrocks when it is not needed? If you don't want to take the time to construct walk through sets, flat sets are your only other choice. With visual attractors added to a flat set, they can be very effective cat sets. Each area of the US has slighlty different methods that have been developed to make sets more efficient and productive. Cats will very often walk right by sets that do not funnel them right to the trap. Again, tracks in the snow have shown this to me. No lure or attractor will make all cats work your sets 100% of the time. Cats with a full belly, cats through hunting for the night and heading to the cliffs to bed down, cats on a cat mission
and wind directions that do not allow the cat to smell the lure, will all add up to cats walking right by anything but walk through sets put where they want to go.