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I bought these for my oldest son's bicycle last year. He loved them so much, I bought a new set for both boys this year as they were getting new bicycles. Unfortunately, they only fit for my oldest son's bike, which is a 16". My two year old has a 12" bicycle and there is no way of fitting the main unit in through the spokes to attach it, so unless you are certain you can remove and reattach spokes, which I do not know if we can do without breaking the wheel, I would only recommend these for bicycle wheels of 14" and up, and even then, it was a very tight squeeze to get these in place on the old bicycle.
However, assuming you can get these in place, they are absolutely brilliant. When we had the boys bikes at the caravan site this summer, my son's bicycle was the hit of the place, with every other child there asking about his lights, and begging parents for a set. Used at night you can see these for quite some distance, and the colours are absolutely stunning. Even in the day, the light is bright enough to be visible, but looses much of its effect. Of course the children love these simply for the bright colours and novelty effect. As a parent though, I do think of them as a safety feature as well. my son is not quite 6, and I prefer for him to ride his bicycle on the footpath around the green, or in the caravan site or something else off road. If a child were using these on the street though, I think they would be a brilliant safety feature making the bicycle extremely visible from the sides ( although visibility from behind is limited). I also really liked the fact that my son could race up and down a large runway at the caravan park at night and I could watch to see where he was easily in pitch blackness.
Each unit requires 2 AA batteries, and I would advise using the good batteries, like Duracell as my husband claims changing batteries is a nightmare. With frequent use and good batteries though we have only had to change them once in the last year. the device itself consists of a fairly large plastic clip and a long tube through which the led lights flash. the manufacturer claims that this product has 25 different colour patterns. I can not say that I have counted them, and it does not seem quite that much, but they are very likely counting similar patterns. It does however keep changing and showing different colours as the child rides about.
I did have some concerns about what would happen if this product got wet. In fact there is currently a review on Amazon stating that the unit is not water tight. In our experience though, this has performed brilliantly in spite of frequent soakings. My son loves puddles - as most boys do, and I am one of those parents who simply does not care how dirty the children get. I just think, I have a bath tub and a washing machine, and thankfully the Good Lord made children very washable. So with a free reign to race through puddles, my son actively seeks them out and has ridden through several very deep puddles, and crashed halfway through a few of them. He has often come home with both himself and the bicycle completely covered in muck and mud, and even adding further water by hosing the bike down has down no harm, although I do avoid directing the hose directly at the unit. Therefore, i can only conclude that the person who had problems with puddles had a faulty unit.
The only drawback to these lights is the price. They cost £9.99 for a single unit, but of course the bicycle has two wheels so you may want to units each as we did. Thankfully dooyoo vouchers covered all four units this year. I give these a complete recommendation, as does my son who still loves these as much as he did when he got his first set last year. His first set is still working well, but as he is still keeping the old bike too, and I was buying a new set for his brother, we left them on the old bike. Too bad his brothers did not fit.