I was looking at that app a few days ago, its based on math so don't know how accurate it would be to the real world swing weights of rackets but it does allow you to gauge how a racket may change with customizations.
I did enjoy the tennisspeed blog article a have been wanting to do something similar but I need to get hold of a higher rate camera then i've got at the moment.
The video below is what I was thinking about doing. I think its just distance over time measurements at various points of the swing. One could do this quite easily using the stop watch function and the size measure tool (measure racket size) for scale in the Kinovea software.
I can start adding lead and take a few measurements to get an average and then repeat this for a few iterations till that racket head starts slowing.
At the moment i'm using an APD and it feels light as a feather so I know I definately can add some weight. I just don't want to add too much as mess up my stoke.