Do you think, in the long run, membership in unions drives

Do you think, in the long run, membership in unions drives the cost of consumer products and services up or down? If so, what in particular would continue to such an increase? If not, why not?
Have you ever heard the expression: “Employees rarely leave their company. Insteady, they generally leave their manager.” What do you think this means and how does it relate to unionization?