Saga is superb for working with grids. Its open source structure and its scriptability make it very useful for our day to day grid manipulation. In comparison to the grid-powers we find that the agility to process vector data is far behind the grid powers. While vector data manipulation is possible to a certain extend, there is one big downside to the module functionalities:
ESRI-shapefile data format is not supported fully
I wish for the compatibility with Z/M-data format, meaning that PolyLineZ shapes could be read and written as an example. I have looked into the source code and figured that in shapes_io.cpp the Z/M-information is simply skipped for the moment. Also the shape object does not seem to comprise a 3d point object. Correct me if I am wrong, but this would be a superb feature addition to have in my opinion.
Best wishes and thanks for this lovely software.