mCaptcha is a proof of work pseudo-captcha, it won't block bots completely, but it heavily rate limits them and makes them computationally expensive to run.
Benefits - costs: If your benefits from having less spam and the work they are doing by solving the task are greater than your costs this is acceptable.
While I'm really glad to hear about it, I think it would work great for DDOS detection, I don't know that it works for preventing spam accounts. I'm pretty sure puppeteer with GPT4 could check that box no problem.