Love it, I would use about a teaspoon for a gallon container, maybe more..it depends how nutrient rich your potting mix is to begin with. I usually don't really measure for a container like that though. I fill it about 1/4-1/3 full, add a big pinch(my hands aren't large so my big pinch could be different than yours) and mix it around a little and lightly pack add more soil or the plant whichever comes first. When I get to about half full I sprinkle a smaller pinch around the circumference and slightly mix it in, add more soil and once it's nearly to the top I add another small pinch mix around a bit, top it off and pat down like I do.
I like to use the Starter-tone for smaller plants, I think it makes a big difference, but Any-tone is better than No-tone.