The Arduino NG has an on-board voltage regulator for use with the coax power jack or the "9V" power pin. Mine has a 78M05, which tells me that (accounting for the protection diode) I can apply anywhere from around 7.5V up to as high as 36V (depends on the regulator, be careful over 20V!) to that coax power jack and the Arduino will be just fine.
If this guy has a switching supply in that box it may be a little more efficient than the linear regulator that the Arduino NG, but you'll also be powering the FTDI chip if you use the USB cable for power so the FTDI consumption may offset any savings.
-j