Not only proving the product was defective but what keeps them from blaming the mod used. If used in a mechanical, it will be said user error by using an unsafe/unprotected mod. Then in a regulated mod, it will be said the mod wasn't UL or certified, so therefore an unsafe mod can't be ruled out again.
That's not even getting into coils be them hand made or drop ins. It will come down to coil failure and consumers using unsafe devices, that should have stopped the battery from venting.
I think a first year law student could easily argue that batteries don't just fail and that it was something to do with the failure of the device it was in.