I think it is safe if you are smart about how you use it. The higher levels are going to be hard on equipment, namely the auto trans. You also need to watch EGTs to make sure you aren't running to hot, the extra fuel will do that. So I think used wisely, it is a very good choice. You might be spending more than 300 though if you need to get a new exhaust probe, and boost bolt, plus the other stuff to hook it up.
On the whether or not to do it... I owned four of these trucks before I modded this last one. I have stayed mild as well and I am super happy with it. It is a total monster on even my 60hp setting, waaaaay more fun than stock. I think reliability is still very good if you use some common sense.