Ok, it may enable others (motorists) to see you on your bike from afar, when you're a speck in the distance, but, does it work when it really matters, when if they don't, a collision will ensue? My contention is that in these circumstances, hi-viz does not work and that you will be seen or not seen regardless. it depends solely on whether they are looking out for you or not. I recall a few years back watching an experiment on the telly. A group of people (a) were shown a film of another group of people ( throwing a ball to each other. The group (a) were asked to count how many times the ball was caught. At the end of the film, group (a) were asked to state how many times the ball was caught: most of them got it right, as you'd expect. Group (a) were then asked if there was anything else they noticed: only one or two of them put their hands up. Group (a) were then shown the same film, but this time were asked not to count the number of times the ball was caught. They all noticed that a man in a Gorilla suit had walked through group ( when they were throwing the ball around: something most of them had not seen first time round. I found this pretty frightening. It illustrated to me that we humans only see what we are looking out for. Of course, we are all different and therefore this will apply slightly differently with all of us, but we all have this filtering mechanism to a greater or lesser extent.