Well let me tell you no app is 100% safe . But there is a fact also if you are downloading an apk ( initial version) it may contain malwares that can exploit your device , but that particular malware needs to be triggered. And that things is generally done by the update option. ( like when you hit the update button the malware gets executed and so on) .
Coming to the parallel space , as it create a separate space for your apps to run , it should not access your private files but it can do as it requests for more permissions to make sure the app running inside it doesn’t get crashed. So you can not fully trust on this app ( from the permission point of view : 3) .
But you can compare this app to sandbox( which is desktop application that provides a separate space for applications to run and anything happen in that space won’t affect your original file) .So in one way it is good to have parallel space like thing.
Yeah now all is upon you. Choose wisely whether to use it or not ( depends on your need)