By Lithium Ion, do you mean Li-Fe? They have a lower power density and a bit less voltage per cell, and are a bit more expensive (not by much). Their biggest (only) selling point which makes them worth it to me is undoubtedly their safety. LiPos (if protected well enough) can be okay but if one does go wrong, you might get a repeat of Chompalot in a worst case scenario. Li-Fes are safer but not much else.