It does charge the 5S, that is what I have - a 64Gb 5s.
The cable is short and a bit awkward and actually not worth even close to the £68 I paid for it, not because it does not function well, but I think the design could be a lot better. The MDI Saga and connectivity in the Mk7 is the most disappointing part of the MK7 for me.
I think I am just going to go back to charging the iPhone using my Belkin USB Charger and play music from the SD Card and not the phone.
The Belkin charger I have is a much neater solution and allows you to close up the flap on the dash.
http://amzn.to/H7GrAlPlus it means I can charge other things using the standard USB port.