I like them, i brought a monkey one for my DS when he was 4 as he developed a need to run off from his pregnant Mum.
I had the regular ones for my DD as they didn't make them back then. I was someone who thought i would never use them but i soon changed my mind, my DD has a medical condition where her arms dislocate very easily . When she was little we couldn't hold her hand while she walked in case she fell as her arm would dislocate, the harness was our best friend.
Back on topic
I have a monkey one and i think they are great , better then losing a child in the shops or worse have them run into danger.