This is a critical question. The legacy.html page is widely considered safe by the jailbreak community (r/jailbreak, iPhoneDevWiki), but with caveats.
The iPhone 4s, iPad 2, and iPad 3 were notoriously difficult to jailbreak on iOS 9 due to KPP (Kernel Patch Protection). Phoenix is a semi-untethered jailbreak that runs on these 32-bit devices. Without the legacy page, installing Phoenix usually requires a computer (Cydia Impactor), but legacy.html allows for direct installation. jailbreaks.app legacy.html
As of 2025, jailbreaks.app legacy.html remains one of the last active OTA (Over-The-Air) jailbreak distributors for the following firmware versions: This is a critical question