Only if your CAPTCHA-like is hurled at every client indiscriminately. Otherwise you'll end up right back where Spamhaus started: maintaining your own list of go

Only if your CAPTCHA-like is hurled at every client indiscriminately. Otherwise you'll end up right back where Spamhaus started: maintaining your own list of good and bad actors. The advantage of a third party service is that you're sharing intel of bad actors.