will it stop automated competition entries

I run regular competitions on my site, but they have been listed by automated competition sites, where people subscribe and these site automatically submit bulk entries on your behalf – thousands of them flood each competition.

The Entry form is gravity forms with recaptcha activated, but it does nothing to stop them. Do you believe adding this plugin would help, or should I try a maths or other captcha challenge?

Thanks

The page I need help with: [log in to see the link]