I own the BakFlip F1 and have been very pleased with it. The built in snap straps to hold eacy section rather than using a bungee is a nice feature on the Undercover, but using a bungee is no problem on the F1. If you don't have a few bungees and straps in your truck, you're not really a man anyway are you?
The Lock on the third panel of the undercover confuses me. Not sure what it's for or why it's needed. No problems, just don't understand it.
The fact that the Undercover "never touches the back of your cab" when folded all the way forward is nice, but also seems to put a lot of pressure on that hinge. (possibly the value of the locking mechanism)
On the F1, the panel DOES rest against the cab of the truck when fully opened, but that panel has auto grade soft rubber trim where it makes contact, and I have truly not had any issue with that.
Both have essentially the same top material, drain tube system, and watertight design. (took mine through a car wash just to see if it held out water, and it was dry)
The Prop Poles that hold the cover up when fully opened have had some problems with sliding on my F1. Not enough to cause the lid to close, but perhaps the Undercover lock also prevents that.
While I am VERY pleased with the F1, I would like to see an Unercover Flex in person to make a real comparrison. They are so similar, I might just go with whichever costs less!