I'm just re-reading GTD and have got to the bit about labelling files using a Brother labeller.
I have hanging files with plastic tabs which take small bits of card as labels and I have stand-up files which come with a set of stick-on, replacement labels.
Writing by hand on these cards and stick-on labels is no big deal. When I need to re-label a hanging file, I remove and replace the little card; I can stick a new label over the original one on a stand-up file.
Maybe I'm misundertanding something. Could someone please enlighten me as to why I need a battery-powered labeller?