I've used my Cooper anchor twice. It has 4' of coated chain on it. 'The first time was at the beach, in a muddy sand bottom. It kept pulling out until I went over to it and pushed it into the bottom with my foot, then it stayed in. Water was a little wavy from passing traffic but not rough or moving (tide).
The second time I used it was in about 20' of water. I eventually let out all 100' of anchor line and it never held. The bottom was hard, shell. The water was a bit rough, 1-2 ft waves and the water was moving with the tide. The couple of times the anchor did try to hold, we took waves over the bow. But it never held for more than half a minute or so. When I held the anchor line I could feel it dragging along the bottom trying to bite. Not being able to anchor forced us to cancel fishing that trip.
I have since purchased one of the folding grappling style anchors. I haven't had a chance to try it yet, though I'm hoping to before winter ends the season. It's only 3.5 lbs. My thinking is that if the bottom is too hard for the Cooper, then one or two of the grappling arms should hold.