Both tea strainers and tea infusers are used with loose tea. How you use loose tea determines if a tea strainer or tea infuser is best.
Tea strainers are best when using a teapot. With tea strainers, loose tea is placed directly in the teapot. Then, the tea strainer catches tea leaves before entering your cup. Simply hold the strainer over your cup as you pour. Some strainers can fit directly into a teapot or a cup.
Some tea strainer and tea infusers come with a bowl to catch dripping tea.