I agree that individual security is given. However, the comparison given here is not completely right: a Google server will increase the login time after each a wile. In syncapp this is not the case (as i understand). So a bruteforce attack is faster in this case. Additionally there are typically several nodes, allowing a distributed attack. Another thing: If enough people using it and having several shares there will exist a lot of secrets. If I'm not interested in a specific person I can just bruteforce against all syncapp users and see what I can find. I know I don't have to use syncapp,