I just got a new Stihl MS390, as I've got access to pleanty of wood to burn (this is my first year). I have some experiance with, and am comfortable running a chainsaw, but far from an expert. This is also the largest saw I've used. The saw came with the regular, not anti kickback, bar and chain. The 2 questions I have are, first, how effective a safety device are low kickback bars and chains? And second, what are the disadvantages to using them?