Alright so I've had the Thule X4 since last Tuesday. I thought I would give my quick thoughts. Some of this will probably repeat what Kristen has said. Oh and this is for the 6 Minus.
I'll start with the one thing that I don't like.
The screen protector -
I'm sure the protection is great, however for me I can't deal with the way that it impacts my use around the edges and how it looks. It's personal opinion of course but I think the screen looks much better without it. It's like night and day to my eyes and fingers. It's just a matter of the value you place on protection vs screen quality. Typing on the edge and using edge gestures are also difficult for me. It wouldn't stick down all the way on the top right corner.
Now on to the good.
The grip -
This case is AMAZING for grip. As stated here before the grip on the X3 was good but the added "nubs" that are on this case are just crazy good for grip. The Phone feels so secure in my hands no matter what.
Everything else-
This case doesn't add very much thickness. One thing that it does add is width (which I like).
The sides are flat instead of rounded which helps with grip but isn't as comfortable(obviously) as as naked iPhone or a rounded case.
This case looks great! Feels solid and sturdy. Not cheap looking/feeling in anyway. And the metal buttons accent the Thule logo very well.
Speaking of buttons, these are much better than the X3 buttons. Easy to press easy to find and great feedback. Some of the best buttons I've found on a case.
Mute switch has good room for the finger but kind of deep given the added width.
It provides great peace of mind to know this thing can take 6 foot drops.
Ports are generous and have a nice touch. They are made from a flexible material. So even if a cable is slightly too big the case will flex to still allow you to still use it.
Last but not least. While this case has a good sized lip, it is far enough away that you can feel the curved edges!! This is one of my favorite features of these phones that is taken away by almost every case. I love being able to feel the curves and use edge gestures easily while still having protection.
I think that sums it up. Thanks again to Kristen and Aron from mobile reviews for making excellent reviews about this case.
Edit: I love this case. It might be my favorite of all time (for now) but it's definitely over priced. And they should sell it without the screen protector.