They are safe, but very uncomfortable. I have not yet met any decentralized exchanges which would be convenient to use. That is why centralized exchanges flourish.
Many projects are currently working on the creation of a new technology of decentralized exchanges. It can probably be said that the trend of 2018.
I think that we will not soon see such exchanges into action, so we should not rely on them, but for now we are content with what we have
I think that many high-quality decentralized exchanges will be launched soon. And these such exchanges will become very popular in the future.