Just got my Defender in the mail today. It's a very sturdy case so far. The installation was a breeze (I used a cleaning cloth for glasses to clean my screen before putting it on). No weird smudges or anything under the screen protector. Everything fits really snug and there's no wiggle. I'm carrying it in the belt holster, and the holster holds it tight. It doesn't feel like it's gonna fall out at all.
The flaps cover all the ports very nicely. Headphone cover is difficult to get out, but I'm a habitual nailbiter, so if you have fingernails it won't be a problem. The volume and power button covers are placed perfectly and all buttons function as they should. My only gripe is that the the covers over the bottom row of buttons doesn't sit flush. There's a bit of a gap over the buttons because it seems there's not a spot to hook the silicon case to.
Overall I give this case a 9/10. Solid construction, great feel, and all the buttons work fine. I recommend this case.