Child leashes/harnesses

My cousin is thinking about getting a wrist leash for her 20 month old son for when they go out. Her reasoning is that she constantly has to chase him around stores and parks and he won't come back when she calls him. (Isn't that every toddler?) Am I out of line for thinking this is ridiculous? I have a very active 2 1/2 year old girl and we've never had this issue. When we're at the store she goes in the shopping cart or stroller and at a park, we follow closely behind her. Maybe I'm missing something?