I too have issues with the tool crashing on large converts, however FSET never seems to.
So currently downloading a huge area, about a quarter of the UK at res 0. It has been dlownloading about 34 hours so far and is currently on tile 270 of 520.
I figure when done I can at least leave FSET alone a while and just use that whole abundance of images to keep doing smaller converts, and always have a larger image than the TMC files to help with issues some of us have been having.