I read a while back that they actually cost you some m.p.g., the only thing that improved fuel economy was the tonneau cover. Surprisingly, they said that having the tailgate down was worse than up, and the mesh tailgate nets were even worse. I have a fiberglass cap on my truck and I still get good mileage, but I guess I'd get slightly better without it. I like it because I can keep tools in the back and they are safe from rain and wandering hands. I got the side windows that hinge up and I can reach in and get to whatever is in there. To remove it is a bit of a pain, by myself it takes about 30 minutes (much easier with two people). Once off, the truck feels more peppy (I've got the four squirrels inline). The cab is also brighter with light coming from behind when it's off. The installers also drilled holes to bolt it on, don't know if that is the norm, but I wasn't happy about that (although it has never come off, but I have seen truck caps by the side of the highway so maybe some aren't bolted on).