Can't say enough good things about this product. We used reins with first child - so she got used to not holding hands and then to running off. With this arm-strap harness, you can hold your toddler's hand and slip the 'leash' up your arm just in case you/they let go. My toddler holds on to the buggy as he walks round town and I have no worries about him getting distracted and running. Another great thing is that there is a handle at the top of the rucksack/harness - so when we're getting on trains, I can just lift him (painlessly) over the gap with the handle, rather than carrying him, so he can keep walking.
The wrist strap is enormous, though - apart from that, this is a quality product.