[daveoflynn]

It took about 30s to ‘solve’ the captcha on my iPhone XR, with minimal feedback as to why it was taking so long.

That was pretty annoying. If I hadn’t been on a site demoing captchas, I would have assumed the site broken and moved on...

[dylz]

After 3 minutes, this just crashed the browser on an old AOSP stock Android device I have. The last time I implemented something like this as a proof-of-work (first party) solution, it fell apart instantly when someone wrote a dedicated bot for it - 5 zeroes were found in sub-0.5s times in non-browser-JS.