Pigs take 2-4 days to die, so this is clearly not a humane poison. It can also kill animals who eat the carcase of poisoned pigs. Warfarin is an anticoagulant. In humans excessive doses cause bleeding of internal tissues and organs. Pigs take 5-9 days to die.
Poisons are a cruel way to kill animals.
They also kill animals other than those intended, both directly through those animals eating baits, or indirectly by those animals eating the corpses of poison victims.