I had some talks with the dev about it and he would rather have missing features than actually require the key sent to his server, if I recall it uses steem connect which is made for steem app authentications and created for local storage of the key, and in this case you will only use the private posting key found in wallet which can't be used for actual transfers :)
I have been using it and feel rather secure
@alphacore you say private posting key but you don't say what else to do. I see the private posting key in my wallet so what is it that I need to do? I have been on Discord on the PAL channel and used it to the upvote channel there. Can you be more specific?