Geeklog ships with a flexible and powerful
spam filter. However, there isn't "the one" way to protect your site from spam, so you may also want to use other forms of protection as well.
The CAPTCHA plugin that you linked to is one such tool. It's still under active development (the article you found was the original announcement). And it's on use here on geeklog.net, as you should know by now, as you had to get past it when you signed up for your account here.
And there are
other tools and measures against spam.
I'd say start with the Spam-X plugin, see how it goes, and then add what's necessary.
bye, Dirk