I would say it's the best addon of this kind... QR code is just a click away. If you don't need any extra features to create your own QR's or edit them - this addon is just for you. The pop window shows nothing but your code. Simple and clean :)
But there is a little issue with it in Nightly 58... If you put icon from main panel to drop-down menu, the pop up window has different size and crops the QR code. Would be nice to fix this.