in this order:
1. It`s safe, never heard about someone bricking because of priiloader.
2. Yes it`s highly recommended
3. Priiloader can recover some bricks, imagine : you install a wad, there is happines all around, but when you go to the systmenu you only see a black screen. "oh no!! the black screen!! but hey, I got priiloader, I can boot HBC trough priiloader and uninstall the bad wad!!! tadaa you are unbricked
4. Priiloader can block the disc ad online updates, so that`s extra protection