p0sixspwn is a one-click utility like Absinthe was for iOS 5. No user interaction at all. All jailbreak utilities have an infinitesimally small probably of your device going sideways, so yes you will have the probability of losing data if your device ends up in a boot loop or recovery loop for whatever reason though I've yet to hear of a situation where it's happened using p0sixspwn, so backing up is a must, as it is the same for each and every jailbreak, and backups should be made periodically, regardless of jailbroken or stock devices