nothing wrong with using a steel to touch up the sharpness of of the knife, though the main sharpening should be on a stone.
being that I use knifes everyday, I use the stone often using the steel only to maintain the edge not using the steel to make or sharpen knife
in the field I'd already have the knife sharp "obviously". a small medium rough steel would be my choice, enough bite to keep the edge but not too rough to eat the blade