I've spent the afternoon playing with my Winkku*.
Since it's an extension to be added on to one end of the handlebars, it's a bit inclined to wobble on its own, which means the rear-view mirror doesn't always give the clearest picture. Of course, that might be because I'm currently using the strap-on** - I'll wait to see if it's any better if I use the version that has to be actually inserted*** into the handlebar.
The lights are bright. From the rider's viewpoint the indicator doesn't seem so, but it would be different from the perspective of a following car-driver. I'm not sure if it makes a great deal of difference to how drivers respond: they seem to have been giving me a wide berth anyway, for whatever reason. I'm not sure I trust it enough to do without hand-signalling for a right turn, just yet, at least; but it's handy that it also makes an extra set of front and rear lights.
*Oh do stop sniggering.
**Look, I won't tell you again.
***Oh for heaven's sake...