Here's my setup:
Perhaps a better view:
So, I've got my Ortleib mount, Cateye and Luxos U switch/USB on the Thorn accessory bar underneath the stem, and the Wahoo RFLKT+ and Garmin Edge 800 on the top bar, which I made myself out of brackets and a length of carbon fibre bar I bought on eBay. Note: There's room on the top bar for a GoPro or a phone/iPad mount, which is my next addition.
Do I need all of this stuff? Perhaps not, but I'm still playing with nav solutions, which vary depending on where I am. The Garmin is reliable, but needs a buffer battery for all day rides, and I hate the interface and built-in maps. The Cateye is my most reliable odometer.
The Wahoo talks to my phone or iPad and to the Garmin (it is a Bluetooth/Ant+ bridge), and displays numerous data fields in a much easier to read in bright sunlight LCD display. I use it with the Cyclemeter app to log my route, times, climbs, etc. to Strava. It will even read my HR monitor, which is Ant+. The problem with the Wahoo is that it is less than reliable, sometimes switching off or losing connection part way through the ride. The phone is close (usually in a top tube case just 25cm from the RFLKT+), so I don't get it. It uses a button battery which is supposed to last a year or more with normal use, but I have found it sometimes freezes "on" and drains the battery unbeknownst.
All of this (except for the Cateye) will hopefully be rendered surplus to requirements if I can get a readable output from my iPad mini, which is being mounted to the top bar in a Lifeproof fre case and cradle. Photos shortly.