The version you play on these sites is often a "hacked" or poorly emulated version of the original 2011 Flash game. It will likely be missing content, have bugs, crash frequently, and offer a subpar experience compared to the official Rebirth or Repentance versions.
Legally, the situation is ambiguous. "The Binding of Isaac" is a copyrighted commercial product. While the original Flash demo was free, the full game is paid. Unofficial "Unblocked" versions often use emulation or reupload the game without permission from the developers, Edmund McMillen or Nicalis. Downloading and playing the full game for free from these platforms, while typically not prosecuted for individual users, constitutes a form of piracy. the binding of isaac unblocked games 66 ez
The Binding of Isaac Unblocked Games 66 ez: How to Play Anywhere The version you play on these sites is
Use the "Fullscreen" button usually found below the game window for the best experience. Gameplay Tips for Beginners "The Binding of Isaac" is a copyrighted commercial product