If you are going to trust them to balance your tires I would use enough to do the job completely. That way if you lose a weight or add a TPMS system, your tires wear or anything else changes the weight of the tire your balance should be ok.
Some of those beans and powders used for tire balance require special inflator valve to prevent clogging. We use the Centramatics on our wheels and love it when tires get changed we do not have to add new beads. After the mh sits for awhile we can feel the balancing take place as we start out. Never have to rotate anymore.
Cost wise however, beads should be considerably cheaper and from the reports on the forums, seem to work very well.