[bpires]

The author did compare their performance with captcha-solving services. His accuracy is comparable to the service with no extra cost to the attacker.

From the paper: "We compare our performance to that of Decaptcher, the (self-reported) oldest captcha-solving service. We selected Decaptcher for two reasons. First, it supports the image reCaptcha, charging $2 per 1000 solved captchas. [...] Interestingly, some of our summitted challenges rejected due to the service being overloaded, and had to be resubmitted at a later time, and received a time-out error as the solvers did not provide an answer in the time window allocated by the service. 258 challenges (36.85%) were an exact match. When taking into account the flexibility, 321 (44.3%) of the captchas were solved. The average solving time for the challenges that received a solution was 22.5 seconds. While the accuracy may increase over time as the human solvers become more accustomed to the image reCaptcha, it is evident that our system is a cost-effective alternative. Nonetheless, our completely offline captcha-breaking system is comparable to a professional solving service in both accuracy and attack duration, with the added benefit of not incurring any cost on the attacker."