Regarding the performance:
After outcommenting obj.redraw() at many locations it's not that slow and can be used for complicated layouts with many elements.
Especially Container::OnChildAdded() and set.Children() with obj.redraw() is a real peformance hit.
So, I'm building the GUI and call redraw() manually after all childs have been added.
Anoher peformance issue is ver('Matlab'). I simply use the old version, it also works in the newer versions.
One problem though:
My figure with a gridflex can not be printed or saved (e.g. as png). I get an error in Mathworks 'print.m'.