The ONE comes with a large suction cup mount, but the mini-USB charging cable is separate, so you have to fuss with the suction cup and the cable separately every time you remove it / reinstall it.
For a few months, I used an adhesive disk affixed to the upper part of the knee bolster, like this (this pic shows my allroad setup, but my S4 setup was the same):
The setup worked well, was unobtrusive, and got good reception, but it wasn't a dock.
While ProClip makes a charging dock, it's large and conspicuous (a suggestion to would-be thieves that you might have a GPS unit in the car, even if you've removed it from the dock) and expensive ($80):
What to do? Create your own dock!
Here's what I did:
1) I found some of these plastic brackets laying around my house:
2) I then took a straight mini-USB cable (I found that the Blackberry cables, which I had a number of, provided the most stability for the TomTom), cut off the large connector part, fed it through the bracket, and secured the mini-USB part to the bracket using a small hose clamp, snipped off the extra metal band after tightening the clamp, and pounded the clamp flat. I then painted everything flat black.
Next, I screwed the assembly into the back of my ProClip clip.
These pics doesn't show all the steps, but give a general idea:
3) Feeding the USB cable:
I fed the cable through the glovebox (neatly tucking the cable into the crevice along the trim piece to the side of the headunit, which crevice is accessible after you open the glovebox) and fed it through behind the dash (over the center tunnel) to the driver's side:
I then cut the original TomTom power adapter, which I had hardwired to my fusebox to a switched power source, and connected the cut-up USB cable to the TomTom power adapter (red to red, black to black).
(Sorry, no pics for this step.)
4) Here's how the final dock works:
The TomTom is sufficiently secure plugged into just the mini-USB connector, it pops on and off easily, and it gets charged when the ignition is on.
P.S. If you're wondering why the TomTom charging cable couldn't be used directly, it's because the L-shape of the mini-USB connector wouldn't allow me to attach it to the back of the bracket: