They’re good, especially the TI-83 and TI-84, but there are calculators from Casio and other manufacturers that will serve just as well. You can store formulas on a TI-84, and probably on a TI-83, and do lots of other things. See, for example, the following YouTube video:
Do you need such a calculator? No; any decent scientific calculator (such as the one you probably bought for chemistry, physics, or advanced high school math) should work.
Author: John Linneball Who did you think? ;-)
I'm the proprietor and only tutor for this business; that's why I named it after me.