@keefmarshall@mastodon.online thanks for the write-up! We do something similar but use Altcha for a proof of work challenge. The stars: Up to 50k bot protections per day triggered, 2.5k challenges solved. No negative feedback from users. So... 95% bot traffic 
Likes
@dmaus
Excellent - yes mine is definitely not unique, nor as effective as a proof-of-work - but the key difference is that it's all entirely encapsulated inside the nginx config. I only have to install this once and it works on all domains served by that nginx instance.
I've got several tiny websites with varying domains, I don't want to have to install challenge files / applications onto each of them!