Before my son came along, I wondered why some parents out there used these for their kids - no judgement really, just curiosity, really. Figured there must be a reason. When my son started walking, I found out why. This dear sweet boy is always in motion... but... oftentimes blissfully unaware of any danger around him... and when we went to the beach, and looked up to see him a quarter mile 'up' the beach, back to us, running at full speed (not much speed, he's 3)... there is an 'aha' moment... suddenly, no explanation of "why do some parents leash their children?" is necessary.
We tried it out a couple of times, and my son does 'lean' away from it from time to time, but hasn't ever complained about it.
The 'Animal' attached to it (ours is the giraffe -- least expensive at the time), doesn't really fit much in it -- it's more for 'looks' than 'cargo space' -- but the harness itself does seem sturdy, which provides much-looked-for peace of mind.
If you have a kiddo that is 'long' on energy', and short on awareness/survival instinct... give this thing some thought. When you do, the next time you see a parent with a toddler on a leash, you can totally embrace each other with the "I totally get it, bro/sis -- I totally get it" look.