I am the creator of the cryptocurrency exchange app, QuatlooTrader, that I released in 2015. 1000's of people used and still use it for trading in the many cryptocurrency exchanges like Poloniex, Bittrex , and others. some people then had the same concerns as they had to enter their private api keys into the application to use it. there has never been anyone to suggest there ever was any dishonesty with that app and it is still used today! Its a judgement call, but i'm not just some nobody coming out of the woodwork without any reputation. All that being said, I understand your concern.
RE: Introducing Steem Exchanger, A Desktop App To Manage Your STEEM Account and For AutoTrading Tokens at Steem-Engine.com