One can see that the
Get operation does work, but simple output is suppressed:
Export["testfile.m", "Print[2+2]; Sin", "String"]
Button["Load", << "testfile.m"]
When the button is clicked
4 is printed, but
Sin is not.
This is the same as:
Button["Go", Sin] which also does not print when the button is clicked.
Get is used directly:
At the moment I cannot recall how to get the plain output printed to the evaluation Notebook.
EDIT: It appears there is no simple way:
Can Button generate output without using Print?