Vet tech here, seconding that the 'slow kill' method is no longer considered a good treatment option by the American Heartworm Society and various veterinary communities. In addition to the reasons already listed above, it means that the worms are still going to be alive and causing damage to your dog's heart for the years it takes for them to die.
Either treatment method has its risks for the dog, but it is far better to have a few months of stir-crazy dog than years of dragging the condition out.
Either treatment method has its risks for the dog, but it is far better to have a few months of stir-crazy dog than years of dragging the condition out.