Why copy it? How is my version different? I HATE how the Engbedded's version uses server side requests to perform the calculations, this meant that the page refreshes whenever you make a change. The URL for Engbedded's version is very long when you use it. My version is also aware of possible fuse bit combinations that may have a behaviour that is not listed in the Atmel part descriptor XML.
Some of the chips may not have good descriptor files, thus the page may be useless for that chip, this mainly applies to the new XMEGA chips.
Read more about it on the actual calculator page.