Of course they are heavy. That means that they will stay put when you put them down. Go for something lighter and more expensive if you intend to move them every five minutes. They are sturdy, so you can sit on them, stand on them, and walk on them. If you can run on them your bed will be too long. They also mean that you can increase the hight as you get more material to fill the bed. They are also useful for partitioning if you want to make small beds for permanent plants or even with a different soil type. I did this with everlasting onions with which I had had limited success until I discovered they like to be planted in clay. Bigal