If you truly cannot afford the Pro license, you have ethical and safe options:
TL;DR: While DiskDigger is a legitimate and effective data recovery tool, searching for "free license keys" online is a trap. The "free" keys found on cracked software sites are typically malicious, outdated, or fake. The software has a genuinely free version that works well for basic needs, but bypassing the paid license for the "Pro" version poses a significant security risk to the very data you are trying to save.
DiskDigger is developed by an independent programmer (not a large corporation). There are no mass giveaways of valid, unique Pro keys. Any key you find published on a public forum is either:
Before discussing the license, it is important to evaluate the actual tool.
User Interface: The UI is utilitarian and dated. It isn't pretty, but it is intuitive enough for non-technical users to navigate.
DiskDigger license key updates offered “free” by third-party sites are unsafe and illegal; use the official licensed version or open-source/free alternatives instead.