I required it for Kunena guest post and registration forms.
The range of configuration and spam blocking options is very extensive. These can be applied to all the places where you could need it in Joomla as well as other extensions and modules.
I had a minor issue with the calc check. Contacted Viktor in support and he answered with a resolution within 24 hours. Great service and support that would put commercial software houses to shame.
After trying (and discarding) 3 other captcha extensions, this product is fantastic and I simply wouldn't look any further.
Thank you for the nice review!