well if you call that working then it might be so.
i call it pretty useless if you adjust for just one end of the focal length....
Great. If you think it is useless then I certainly don't recommend getting it for yourself.
I have a 70-200 f4, 24-105, 17-40 zoom lenses and focal has worked like a charm for me on my 1DIV and 5DII.
If you are like me (which I am not saying you are) I tend to shoot at the max end of my focal length on my tele zooms. Because I shoot here 90% of the time then it makes sense to calibrate my lens for the longer focal length. If you are a shooter who uses the short end of the focal length often you could just calibrate it for the short end using FoCal, remember the MA setting, and change it manually when you are going to shoot at that shorter focal distance.
I have the MA adjustment menu on my custom functions menu on my camera so I can easily adjust the MA on the fly. FoCal will help you determine the optimal MA setting for any focal lenght and you can simply change it as needed if you are using using a specific range on your zoom lens.
Also, at very short focal lengths, unless you are shooting really really close to your subject.... the wide depth of field renders the MA argument moot. If you are shooting at subjects very close to the minimum focusing distance then it is VERY important that the optimal MA setting be accurate at that short focal length.
Every shooter uses their gear differently and for me, FoCal has been priceless. We have only begun to scratch the surface of the uses of this software in this thread. I have done testing to compare WH200 setups to sidekicks, hand placement locations to mitigate vibration, etc....
Just make sure you shoot in a controlled environment with a consistent light source. I shoot indoors with two 500 watt floodlights on my target. The literature with the software explains all of this very clearly.