The MintEye CAPTCHA was invented by Shayke Inbar, one of the company's founders. Inbar has dyslexia and found it hard to do the standard CAPTCHA tests.
The MintEye software makes using CAPTCHA less frustrating for some people and it might also be a bit more secure in one respect: computers can be programmed to recognize distorted letters. MintEye would be less vulnerable to that kind of attack.
Even so, it is possible to write software that would detect when the slider is at the right point by checking for straight lines in the image, though that kind of software is harder to write.
MintEye isn't just about security, though. It's also about advertising. The images MintEye uses could be ads, and that's where the company makes its money. Some CAPTCHA systems already have ads; MintEye says that because the user is deciphering the image of whatever it is being sold, the brand recognition will be stronger.