I use it as well but I have to admit that I don't like the fact that they know your private keys
We know sometime that the era of centralized exchanged is fading away. There are simply just too much hackers and too much counterpart to risk with traditional exchanges. I had read some articles that contains about the uses of this EtherDelta for it said that it could be a trustworthy so we can trade here token's safely. But it actually doesn't matter if we trust it or not.The choice is up to us.
studying and reading information about the platform that we will going to use is a must as for me ED can be trustable to use in terms of exchanging our tokens
its safe from my own experience I do deal with maybe .2btc worth of tokens and it went fast and no problem from my side so in order for me to use the platform
I need to provide my private key I haven't encounter any issue with that.