i have not noticed a loss or a severe increase in temps from my hoods by using one mine was about 6 feet. most fans are inline fans an designed to go inline ducting so i dont think the resitance of a muffler will hurt you unless you are going to a size reduction in ducting.
No size reduction, but I am pulling the air from a window well. Just have noticed some cfm loss since installation of my mini can muffler. I'm going to check the well tomorrow to see how the filter looks could just be pretty clogged.