You can also use ACC20 to get 20% off ($6). If it's still working, I used it yesterday after seeing it posted somewhere around here on the forums.
The vehicle mount also does not come with a car charger so you can use CHR15 on the vehicle power charger and get 15% off ($3.37) Unless the code the op posted works for the power charger then use it instead.
Also note that the car charger is already at a discount price online, and taking an extra 15% off took it down to about $20 total.
With 20% off the vehicle mount it totals around $25.
I found the CHR15 code on retailmenot.com. I recommend checking that site out for discount codes such as these.