Until the first production K2s ship, we have no idea what the Vf will be. So at this time we can't say. If the K2 is available with the same bins as the Lux3 it should be fine. The K will also handle a far higher drive current, so if you drive an SxxK bin K2 at it's nominal drive current it shouldn't be damaged by the higher current you'd get from cells hot off the charger (you'd have to verify this though).