Unfortunately this service did not block any of the spam registrations I was getting on my website. Also, there's virtually no advanced options in their 'dashboard' just a list of accounts that successfully registered for my website (that were spam). No whitelisting/blacklisting, block by country, or anything else you're really come to expect from an anti-spam service.
I've had my own issues with cloudflare, but you'd be better off with their free service (which has the options mentioned above) than paying for this service that doesn't really seem to work.
We have released new version. New version has option for check messages from new users.
You can test it and if you want we will be able to offer you to use CleanTalk free as compensation. Please, email us welcome [at] cleantalk [dot] org