Usability testing is more like brainstorming. Those 3-5 users may tell you what some usability issues are - but they won't tell you how big those issues are, fo

Usability testing is more like brainstorming. Those 3-5 users may tell you what some usability issues are - but they won't tell you how big those issues are, for your purposes. With imperfect a priori information on who the users of your thing are, you have to go back to assumptions.