From my experience with these inexpensive load cells he's going to need a gain around 500 (set with 100R) to 2000 (set with 25R). That's a range of just 75 ohms so it's really helpful to have a low ohm pot or you'll go nuts swapping resistors in and out.
Also, considering the Arduino's 10 bit ADC, the imperfect load cell with an existing offset voltage, and the voltage range of the InAmp, he'll only get about 400 points of precision to measure with. It's really helpful to be able to set the gain within a few ohms to get reasonable precision.