I've got a few friction shifters knocking around but all seem so rough as to be impossible to use on a bike. Are they meant to be like that or can a service be done on them to get good use out of them?
Based on my personal experience with friction shifters, they are relatively easy to keep serviceable. Mine have adjustments to add or reduce friction which I generally leave set to a generally usable amount of friction between maintenance cycles. The level of friction should hold them in place, but it shouldn't be a workout to shift gears. Maintenance for me mostly consists of replacing cables and the tubes which the shift cables travel through, along with some cleaning.