If I lived in the States, especially in the lower 2/3 of the States I would likely feel differently.
Yeah of course I forgot that disclaimer, it comes down to where you live. But if you're anywhere south of Maine and Alaska in the continental US, my opinion still stands. If not through the winter, absolutely through the summer...although it just takes one tiny mosquito. Just one.
If I lived in the artic circle or up in the great white wilderness, I probably wouldn't be using it either
But you couldn't PAY me to skip 2 months, unless there's 10 feet of snow on the ground. I guess when you personally see the damage heartworms can do, and how highly preventable it is...