That site has good information but they didn't say what your dog has to go through if it gets heartworm. They have to be injected with a type of arsenic more than once.
It is quite serious to get heartworm. I don't like the drugs either though. If you are in a state that freezes during the winter I would not give it in those months. There is also a grace period for some of them. Heartgard, for example, has a 15 day grace period. They just tell you to give it every 30 days so you remember.
I would probably give Heartgard every 40 or so days because 45 is cutting it too close. I use Interceptor though and I'm not sure of the grace period on it.