A good basic "math" Captcha, but with a few minor drawbacks:
First, even though you are given the option of using "words" in place of digits (ie: "five", "nine") users can't answer using words (which might be confusing). Not a big deal, but clumsy. I simply uncheck "Words" as an option. But a "words-only" Math Captcha might thwart more Bots if users must answer in "words" as well.
The Captcha is ONLY math, no "text" Captcha, so if you want a text Captcha too, you'll need a second plugin.
It would be nice if "/n" (or something similar) were supported in the Captcha Title for carriage returns so your entire prompt/instructions doesn't have to fit on one line. (Maybe some [BBcode] too?)
Biggest problem: If the user enters the wrong answer and goes Back (as instructed), their entire post is gone and must be retyped. That could seriously tick off some people after typing a long comment only to lose it because "butter fingers" hit the wrong key.
Maybe in the next update?