This effect makes the length of all the destination paths the same as that of the source path, while maintaining their shapes.
The source is the topmost path in the selection.
Copy paste_length.py and paste_length.inx in the user extension folder. The extension folder can be found from Edit->Preference dialog in the System option. You will need to restart inkscape after the files are copied.
The effect is under Extensions->Modify Path menu. 'Scale From' value is the origin point of scaling. Scale Factor applies additional scaling on top of the copied length. Precision is the degree of accuracy.
Quick Introduction: https://youtu.be/L7Z48mZlhV0