Most brick layers finish the joint with the edge of their trowel - many different types of joint can be found, some with good resistance to rain, and some more decorative, but with less resistance to the ingress of water, and better suited to inside work....
Jointing tools are often used for repair work, i.e. refilling old joints, or top quality work, where a team of brickies may be build the wall, but leave the joints struck back, so that one can fill all the joints to the same standard, or with a different colour facing mortar.
In the UK, the tool of choice use to be a piece of broken galvanised steel from a bucket handle....