Works every time.
The ones that are impossible for my are the street signs, and after that all of the cultural ones (I see US captchas and when asked to select a sandwich or a recreational vehicle I'm doomed to not complete them).
An interesting side effect of failing a captcha is that to Google this looks like proof the captcha is working, that you're likely to be a bot, and that they should definitely give you the hard captchas.
As such, if you cannot complete a captcha the chances increase that you must now complete multiple difficult captchas.
The audio captcha is delightfully simpler though it does take a moment longer to complete.
I could be wrong though
Have you tried recently? They have gotten way better. There was a time not long ago where I would have agreed with you (the CAPTCHAs were literally impossible for a human in most cases).
CloudFlare has toned the CAPTCHAs down a lot recently, they're now presenting image classification tasks (select street signs/bodies of water/storefronts/cactuses/...), and in my experience, my success rate is close to 100% on those.
Admittedly they still make me solve three of them and they get tiring, but at least they're not completely cutting off access to Tor users anymore.
Am I supposed to click the tiny corners of signs in another square? If it is a sign that is not a "street sign", such as a billboard, do I click it?
::confused::
I just give up immediately when I see a Cloudflare captcha page on Tor.