I paid full price, $13715 including installation, for 2 Powerwall2’s. But at the time PGE had a generous rebate (SGIP) which eventually paid for a large portion. I’m not aware of any particular safety issues, though I’m sure I could find lots of opinions online if I cared to. Nothing is 100% safe, your phone battery could melt down in your pocket. From my perspective I trust Tesla engineering more than other battery makers. They are in my garage next to my much larger Tesla battery in my car. Certainly I feel like it is safer than having a similar amount of energy stored in flammable fuel for a generator. And safer than not having backup power.