"controlled access to source code"
Now that is a nice term. Is there perhaps a tool-chain included to make sure this code really compiles to the binaries they got? Otherwise "controlled access to source code" could well mean - "we edited out the stuff you are not supposed to see, before we handed it over".
But my guess is rather that it means "we can show you printouts which you can search while we are together with you in a meeting room and we'll collect everything afterwards" - good luck finding anything in this heap of paper!
Oh well, I guess I haven't got enough faith in humankind. Oh, wait - megacorps and gouvernment agencies are non-human entities, right?