My thoughts...
If it's going to save your child from getting lost or being hurt (or something alot worse) they are worth every penny.
I have a velcro arm strap one. One end goes on the youngin, the other to me. However I used it when the older three were littlies. I had the youngest IN the pram, and the older two walking either side of the pram. I would put a wrist band one one walking child, wrap it round and round the pram handle over to the other side, and then attach it to the second child. So they were both attached to the pram. I never once had a runaway while out
Some people made comments about it being inhumane to "tie up" my kids. I seen it as mine were right where they were supposed to be.... pity about the person who made the comment... her's would run amuk through department stores, and even run away when she was out shopping!! So who had the better idea??