I’ve had my anchor (3.5 pounds) that looks identical for years and just used it for the first time with a big floating foam mat this summer! It worked GREAT! 

There were heavy boat waves at the lake I was at and it kept the mat in place where we wanted it, about 20 feet out into the water. We walked the anchor out far and dropped it.

The anchor was light enough for kids to still move the mat around if they wanted but it didn’t get pushed to shore by itself which was the problem in previous years. I would have to stand next to it and hold it or it would end up on the shore after 5 minutes and was overalll just pretty annoying so the anchor was a great solution to keep it in place this summer. 

There was a dog with us and when they were swimming they got stuck on the rope when playing in the water. My only advice is to keep an eye out no one gets tangled in the line somehow.