I just got this fancy tea infuser in the mail today, I've only used it once and I'm already in love. It fits just right in my mug and is soooo much easier to clean out than any tea ball or such that I've ever used. Plus it is supposed to let the leaves open up more than a small ball, and that is supposed to be good. Plus the super fine mesh means no escaped particles.
I'm a tea heathen that heats my water in a mug in the microwave and don't ever make sure the temperature is just right for whatever kind of tea I'm brewing, so by no means an expert. But, if you are in the market for a new tea infuser, I highly recommend this one. I actually got a two pack so I can have one at home and one in the office. I know another company makes similar ones with no plastic.