I've always used them in a collecting-dust-in-a-drawer-way. Now, I know HDDs in notebooks are somehow protected (my notebook through a bunch of bangs of all kinds and never complained), but I'm not sure about the external models (talking regular kind here, not SSDs). Had a WD Passport for a while but it seems so fragile (most others do as well).
Is it appropriate to have a few of those things, for carrying around in your bag with your notebook, and camera and expect it to last a reasonable amount of time (>2 years)?
The bag and the drive will not be throwed or anything on purpose, but it will take putting in trains in compartments, up above the seats, carried around, putted on a floor in gentle and not so gentle ways and so on. The regular the life of bags and backpacks stuff :-)
They will be, in a way, my working drives, since the one I have installed in my notebook is too small (1Tb), and I need extra storage space. So I will not actually be having backups of data gathered every day (backups will be carried out maybe once a month).