Re: No public code review --> security by obscurity.
So when it comes to the question of "is it secure?" there's no special practical advantage for open source.
Err, apart from the advantage that you can actually look at the source to answer the question, if it is important to you...
But (as I think closer to the point you were trying to make) that doesn't - by itself - mean the answer is any more likely to be "yes".