Hi, author of the plugin here. Sorry for picking this up only so late, but rest assured that all problems have been resolved already. I was away for a good part of last year, which explains the lack of support during that time. I apologise for that, and feel free to use the plugin, I’m still maintaining it!
If it serves you well do give it a positive review on the WordPress plugin directory! 🙂
I’ve created an add-on for ACF v5 for a reCAPTCHA field type. You can find it at https://github.com/irvinlim/acf-recaptcha
The plugin makes use of Google’s reCAPTCHA so you will need create an API key there first.
I had just created an add-on for ACF v5 that allows reCAPTCHA on frontend forms.
Check it out at https://github.com/irvinlim/acf-recaptcha, do let me know if you encounter any issues!