You pay once and own that version forever (no monthly subscriptions).
Pirated versions often have modified code that can cause your SMTP server to be flagged as spam, destroying your sender reputation. Sendblaster Pro 4.4.2 License Key
Access to the help desk if things go wrong. You pay once and own that version forever
Integration to see who opened your emails and clicked your links. leaving your database vulnerable.
Email standards change constantly. A pirated version won't receive security patches, leaving your database vulnerable.