Using a crack is software piracy, which is a form of copyright infringement. It is illegal in most countries and can expose you to legal action from the copyright holder. Ethically, it deprives independent developers like Andreas Baumann of the revenue they need to continue supporting and improving their software.
Their mission:
Using a cracked version of Z-Cron, especially one claiming to be "top build 09," carries significant security and operational risks: Linux malware persistence using cron jobs - Facebook zcron 50 build 09 crack top