Every obscure browser I've thrown at it has passed except for Opera Mini because it doesn't support real Javascript. Compared to the alternatives (Cloudflare/Google RECAPTCHA), compatibility is great in my experience.
If you're one of those NoScript people you'll probably end up stuck unless site admins enable the meta refresh challenge. If it proves effective, that may get turned on by default in the future, though, which would solve that problem too.
