According to the Open Source Initiative (the folks who control whether things can be officially certified as “open source”), it basically is the same thing as Free Software. In fact, their definition was copied and pasted from the Debian Free Software guidelines.
Nah, when the user wants to ensure trust and integrity in his own system, it works just fine. The problem comes when the user who needs to be able to access the data is simultaneously the adversary who needs to be stopped from accessing the data.
In other words, it’s one of those situations where the fact that it’s hard to manage is a gigantic clue that it’s wrongheaded to try to do so in the first place.