Photo of a Stainless-Steel Tea Infuser by Pengo
This is a type of tea infuser that I commonly see, and very much dislike.
The holes are tiny, which doesn't give enough space for water to flow in and out of the ball. Tea thus seems to infuse very slowly when using one of these infusers...and a lot of the flavor actually gets trapped inside the ball.
When I've tried using tea balls like this to brew tea, the tea always comes out tasting much weaker than I'm used to, even with a long steeping. This is particularly true of the whole-leaf tea that I most enjoy drinking.
Although I prefer basket infusers, if you're going to use a teaball, I recommend one like this one; they're much better.