Can someone confirm what the current state of play is with lipo batterys in heavies? Why aren't they able to be used when they have been well proven in featherweights to be a stable battery that can take abuse and still not burst into a hot flaming mess?

I ask as I'll be looking to buy batteries for Smidsy in the near future and don't want to waste my money on A123s if I can go ahead and use lipos.