I am using your plugin on several of my websites and I absolutely love it, so first off great job!
The only issue I have is that it doesn't fully prevent SPAM in the sense that bots can SPAM the subscription form with fake addresses, and although they won't 'register' as such as a subscriber, it still doesn't stop emails from bouncing back and clogging up my mailbox due to the fake 'invalid addresses'.
As your plugin doesn't natively support Captcha, I looked at several other generic captcha plugins that I could use however I couldn't figure out how to get them to work with your plugin.
Question -> Is it possible to implement captcha support in your next release and/or is it possible to include another plugins' shortcode into your widget somehow to add a captcha field externally?
Thanks for your help mate.