Sorry for bringing up and old thread, but wanted to add that is was SourceGuardian 2 that was easy to revert back to the original source code, because it did not compile to bytecode.
SourceGuardian 4 does compile to bytecode and is much better than version 2 was. I've bought version 4 over ionCube because it has an OS X client, and the ability to bind your scripts with license files with many binding options, both things that ionCube does not offer yet.
I have not seen or even heard anywhere that SourceGuardian 4 is crackable (if you think it is, I will be happy to send you an encoded script for you to try). It may be possible to get *something* from the bytecode just as one might do with ionCube or Zend, but one cannot get back the original source. Suffice to say, SourceGuardian 4 now seems to be on par with ionCube and ZendEncoder.
ionCube is just a useless garbage thing. I did use ionCube license file but it was easily decoded to expose all license properties and the code was php5 OO with obfuscated settings and they were deocded. I am thinking to move away to SourceGuardian.