We have been using these on and off for the last 15 years. As of late, we have been hunting in many fast-moving currents. The current will be anywhere from 5-10 MPH. Standard round weights (egg shaped) will just keep sliding along the bottom, and your decoys will eventually float away unless you are using 8-12 oz weights.
With these J-Weights, they drag along the bottom and are able to catch on rocks, mud, or grass on the bottom and give you much better-holding power than you get on a standard-shaped weight. It's like adding 4 extra ounces to whatever size weights you are using is current. If you have to carry your decoys in any distance, this weight savings really add up.
I also love the fact that the rubber keeps the weight securely attached to the keel while in storage, so your weights are rubbing and damaging your other decoys.
Many companies claim they have tangle-free decoy designs; it doesn't matter if they are clipped onto a carabiner. However, they will all tangle and become a pain in the bottom when it is 5F, the wind is blowing, and you are 10 minutes to legal. These J-Weights are the only solution that I have found that are genuinely tangle-free because each weight and length of decoy line is securely attached to the decoy, so you can just keep grabbing them and throwing them into the spread.
I would highly recommend these for people that are hunting in swift current. (don't use their pvc decoy cord, it will break at the worst possible time.)