I just bought the Retro-Solutions 35 watt digital kit with the vehicle specific set up for the 2012 Focus. Everything works great and I'm showing no errors.
New ford cars absolutely need the harness with the relay or else you're asking for trouble. So spend the extra few bucks.
At first, figuring out how to hook it up can be somewhat confusing but if you have any basic 12v knowledge you shouldn't have a problem. Take your headlights out, then map out the harness on the kitchen table. It helps to make sense out of it. If you need to draw a schematic for yourself, do that too.
If you know how a relay works and you know how a resistor works, you can install this yourself. If you don't know, then take it to someone who does.
I haven't mounted my ballasts yet though. Does anyone have any suggestions on good locations?