Yep, I strongly recommend one. That or go ahead and get a Scanguage which will do the same and give you a lot more info, like trans temp to be specific. It's worth the price for that alone in my opinion. Anyway, all the cheap scanners will do the same thing, read the codes. I really see no reason to buy one of the more expensive ones.
Depending on your vehicle's year I'd recommend one of the "better" versions, the most important to me would be ability to cancel codes----the cheapest tend to not have that feature, are "read only" devices.