Before ordering my Bak-flip G2, I had been seriously considering the roll-up types like those. So I went to a local 4x4 shop and checked out their display model. Here's what I found.
1. Look great.
2. Work great as long as you remember to keep the strap anchored where you can reach it to pull the cover closed again, otherwise you have to climb up into the bed.
3. Have to keep them cleaned off (leaves and other debris) otherwise it will all get into the canister and who knows what that could mean.
4. Water will drain through the canister. But snow and ice will not until they melt.
5. HUGE hassle if you want to take it out for carrying something that takes up the bed front to back.
Based on my observations, I just couldn't justify the cost. You may feel different.
I went for the aluminum folding for security (once its closed and tailgate is locked it can't be opened without serious effort like a pry-bar), strength (fold one panel back and I can stand on it), keeping my stuff dry.
No cover will help with mpg because your truck already has good aerodynamics plus the added weight will overcome any benefits.
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