As I said, that doesn't make it stronger, just different.
It's harder to use OCR on a random deformed text then on normal text but with more variate chars.
I've investigated this a long time and this is the strongest solution.
Notice how many big companies are using it, including developers that offer external CAPTHA systems. Then compare it with how many are using math CAPTHCA or similar solutions.
I understand some users want variety and that is why I've implemented that plugin.
Will try to add more CAPTCHA solutions in the future releases but can't tell you when. Sorry.