Washed Pea gravel is slightly heavier, and far less messy. A 25kg bag is about $6 at Home Depot.
The Ader sandbag is expensive. I was going to get the large Ironmind sandbags, but the Canadian dollar was very low at the time. I bought 4 heavy canvas surplus navy sea bags for the price of one Ironmind. They are a great economical option.