Hi Michael,
I have been using Mint since 2012: it is a great tool and no security issue. It doesn't mean that nothing bad will happen: I think setting all your bank accounts with double identification is recommended as Mint just read data and anyone wanting to login for transactions will have to pass the double-identification. Anyone else has an opinion on security?
If you like Mint, you should also check Personal Capital: it is also free and many BP users seems to like, as well as the FIRE community, for its retirement features. Personal Capital encourage you to use the Advisors / Account managers but it is not an obligation hence you can disregard these messages.
So far, these two are the best I have tested: they are great for people who want to track budget and net worth without the manual effort. If you are a analytics geek like me, you can still use the summary data from these applications to do you own analysis / tracking.
Good luck to you.
Vincent.