So I've got a Garmin, two lights and now have fitted an 'out front' mount for my iPhone. To accomodate that, I had to move the Garmin mount (which is also 'out front') a couple of inches to the left. This means that when the Edge is actually on the bars, I can't ride with my left hand on the top of the bars.
(why does 'out front' not actually mean 'longer than 2 cm'?)
Also, to get the two Cateye front lights out of the way, they're slung under the bars, which means than when an Apidura bag goes on there, they're going to be obscured.
I know that an accessory bar is sort of anathema where a lightweight road bike is concerned, but I need one. Can someone recommend a very lightweight one?