Funny how the 2 Nillkin cases the OP talks about are the exact 2 I bought online.
I bought the white Fresh, and Yellow leather.
Anyway, after having used both, now I know that flip covers, despite the protection it gives, tend to get in the way of general use. Answering calls involve one extra hassle step.
Taking pictures, you have to roll the flip cover up into the triangle as if you are going to use it as a stand and hold it in your left hand, because simply flipping it and folding it over will obstruct the camera.
Nothing wrong with the build quality...I am sure it is better than most cheapos out there. All the useful ports are left uncovered (one of the reasons why I chose Nillkin...there is actual thought process that has gone into the design). If you want to use the magnetic charging port, not many other manufacturers apart from Nillkin make them uncovered.
The yellow I chose is less vibrant in colour (than what it seemed on screen), and does not go so well with the white ZU I have, so that got retired until the day I get SBH-52 and leave my phone in the bag.
For the Nillkin Fresh, I got in white, and am very happy with it, and currently in use.
It has a nice tight fit, seems to be made of good tough plastic, and the texture on the back helps with general grip.
I did make one modification to it, because even though the magnetic charging port is left open by design, it was impossible to get a good connection while the pone was still in the case. So I cut off the thin strip that runs along the screen side of the mag port. Filed it down with nail clipper file, and now it is perfect. It has not lost structural rigidity.
The number of times that i thought that I had closed the USB port properly, but was still slightly open (thus not making it fully waterproof) has prompted me to get the magnetic charging cable. I knew it was something I wanted while I was out choosing the case, so for those who are still looking for cases, I won't say go Nillkin, but make sure you go for one that has the magnetic charging port uncovered.
Whether you buy DK-30 is a different debate. Some like it, but some find it expensive for what it is. There are not many covers out there tat allow you to dock with it on.
But the USB magnetic charging cable is something I believe every ZU owner should have. For that reason get a cover with the port uncovered.