@nedd1e_h: "Please remember that 'reflectives' only work when lit up by the headlights of the vehicle whose occupant is trying to observe you."
Spot on. AFAIK they use the same kind of retro-reflective technology that is in 3M Scotchlite tape and fabric. What it does is in the description: it reflects light back in the general direction that it came from, with very little scatter. That means that if the observer's eyes and the light source are not fairly close to being on the same axis vis a vis the object being observed then the bright retro-reflection will not be seen.
For this reason I'm a little skeptical about retro-reflective jackets as a conspicuity aid in town. They do next to nothing useful under street lights, and dipped headlights very likely won't illuminate a jacket directly (unless you're on a recumbent, I suppose), so the driver won't necessarily see any retro-reflection*. I'd suggest that retro-reflective trousers or shoes might be more effective in town, though I don't know if anyone makes such things.
In full beam headlights, though, a retro-reflective jacket works brilliantly, so I can see a much stronger case for wearing one on rural roads. There is, though, the potential downside that a driver will see an approaching cyclist in their full beam, dip their headlights out of courtesy and - pouf! - the cyclist 'disappears'...
FWIW I do have patches of scotchlite black and silver tape on my black and silver bike, on the forks and frame. They are nicely unobtrusive under daylight, but shine brightly when illuminated at night with the caveats noted above - hence I also wear a hi-viz jacket and helmet, and carry lights various.
* I suspect that this might be at the root of the evidence given in the careless driving case being discussed elsewhere at the moment, that the cyclist was wearing a 'black' jacket. Not that that in any way excuses the actions of the driver, of course - it was pure whataboutery and victim blaming by the defence, and the barstewards got away with it.