I have a Bakflip HD cover on my truck
Fuel mileage isnt affected I don't think personally
But for me its important for storing things. Plus with the autolocking tailgate on the 2013 model is nice so you don't have to be continuosly locking and unlocking the gate with a key
Mine now has the Bak Flip F1. Since I just got my truck and have not gassed up yet, I cannot offer real world comparison. I did read a rather extensive test on mpg with and without tonneau covers. The conclusion was a slight savings in fuel, maybe 1-mpg better.
For anyone interested in getting a Bak Industries bed cover check them all out (these are our advertised prices to get a price with the forumZ discount included please contact us, via phone @ 855-432-3278, text @ 816-686-2176, PM me, or chat with us on our Website