I think it's 6 of one and a half dozen of another. They're basically the same. Every footprint calculator I find, including Evaluating Your Eco Foot Print, has a similar take on the measurement. I would recommend that if you are looking to continuously improve your footprint, you use the same measurement device each time you reevaluate. This will assure that you are comparing apples to apples.
This site's take on things is unique in that they offer the opportunity to measure your personal footprint, a business or municipality's footprint, etc. These variations could be useful in your work considerations. I hope you'll let me know, if you found this helpful or insightful in some way.
I like to offer these opportunities occasionally, as we all come to that point in our lives at different times, when we are ready to know how we impact the Earth. The way their site states it is "How much land area does it take to support your lifestyle? Take this quiz to find out your Ecological Footprint, discover your biggest areas of resource consumption, and learn what you can do to tread more lightly on the earth."