There's a small bump in mileage and HP due to not turning the big fan all the time. The AC is better at idle and stationary due to more airflow through the stack, but that probably won't matter to you in BC. You will never hear the howling of the big fan again. You can turn the fans on before you get to a big hill or when the temps start to creep up if you're towing.
These fans will NOT move as much air as the stock mechanical fan, so there are disadvantages too. Some temps like trans temps will be higher and you have compromised your total cooling capacity so you should not tow real heavy. I've towed up and down the east coast with a 12K fifth wheel, 4 people, 86 gals of fuel, firewood, etc... with no issue, but I have a LB7 which are notoriously cool-blooded. I'd be more cautious if I had one of the newer duramaxes, especially a LLY, which are prone to over-heating.
