dependent for existence, occurrence, character, etc., on something not yet certain; conditional (often followed by on or upon): Our plans are contingent on the weather. 2. liable to happen or not; uncertain; possible: They had to plan for contingent expenses.
But they don't do a worse job, either. Sure, expensive bristle brushes allow you to spread the varnish out smoothly, but so does a forty nine cent foam brush. So it makes sense to use the lowest-tech, least expensive tool to do the job.
The technique -- A fan brush is effective at redistributing powder or foundation and providing subtle shading. Think of it as an airbrush for your face. Polish small areas with a tapping motion or a slight sweeping motion over an area that's a little longer than the width of the brush head.