I bought one, thinking I'd use it with extra spirited and ultra fast Oscar.
The only times we actually used it was in a cemetary when he just over 2 yrs and there were crowds and candles in glass lamps everywhere....this was at Warsaw Uprising celebrations - remembering his great grandpa. Other than that, I used it at the metro station when heavily pg in winter with Emma, so Ozzie 2.5 ish and me slower and slower and the ground icy outside and wet inside. Buggy wasn't an option as the lift was very often broken so it was easier to get to work (preschool for him at the time) by using the steps than by asking someone to carry the buggy.
Also used it for a few more months with him after E was born (until I got my PandTs) if we were out walking and she was sleeping in the carrycot oldfashioned pram. Oscar actually gained road safety skills around a year ago only but finished the darting away by 3.5 for sure. Unfortunately, PL drivers are notorious especially for the right filter lights at traffic junctions. Pedestrians in the middle of the crossing, when the green man is showing, have been known to be run over due to the filter light allowing cars to turn and drive over the crossing "as long as its clear".
My mum never needed one for me - I was a spirited but scaredy cat touchy kid. My sis was the angel with fearless spirited wings and spent many months on a harness.
I've never used it for Emma though....not even once. The harness was placed in our cheapie Ikea highchair when she was a few months old and has been used for this purpose ever since. Much easier when you only have to concentrate on one kid. Emma is much faster than Oscar but is scared of cars and roads, thankfully....and metro tracks too ;-)
I think a lot of our opinions are not based only on the spiritedness of our kids but also the environment in which we live, the amount of walking we have to do and our physical fitness/pg or non pg state.....mine for sure :-(
S x