Here in the Carolinas the li-pos out number the nickel batteries at most tracks and I have yet to hear about a li-po blowing up, catching fire, igniting or even burning. Now we have swelled a few up that went out of balance or was over discharged that includes the expensive batteries in the plastic box too. The swelling makes it alot better the nickel batteries because the li-po will warn you way in advance with a problem compared to several of the nickel batteries that just popped with no warning at all throwing hot metal shrapnel like a grenade......very dangerous with no warning what so ever!!!
Li-pos are safer than nickel batteries anyday when both are handled by the manufacturers instructions.