We have made the app in a way that it only accepts you Active posting key, this way the app 100% cannot make any transactions for you. And if you want you can always change your Active posting key with your master key in Steemit. So in a way you are never under any risk of losing funds.

There are many apps build on top of Steemit blockchain such as Steepshot, eSteem, Utopian, Minnowbooster, etc. I think all of them make Steemit a better place, so it is always up to you to decide what to trust or not. We (SteemApp) are not motivated to harm Steemit or it's users in any way.