New owner of the Kahles 1-6x here. I've owned a lot of low-powered optics, but never the 1-6x MK6 so I can't compare the two. I did own the 3-18x44mm MK6 and wasn't impressed at all. I too think the MK6 line may be a bit overpriced and underwhelming.
As for the Kahles, my first comment to people is that it is the closest thing to low-powered optical perfection I have owned to date. First and foremost is the amazing field-of-view at 1x. It's like popping on a VR helmet. I haven't lost ANY speed when compared to my Aimpoints, and I always did before. I feel like I can't say enough about this. It's a feature you can't read about. You just have to experience it.
I would also argue SFP is actually an advantage in this magnification range. The reticle stays HUGE at 1x, and makes seeing it very easy to find during fast shooting or complicated target backgrounds. This is important because battery-life on all these scopes completely sucks when compared to most red dots. A huge reticle at 1x helps eliminate he need for illumination. I don't want to depend on illumination is what I'm saying, and I don't have to with this scope. I chose the SM-1 reticle. And I also don't mind using my hold-overs at only 6x because if the target is far enough away to require a hold-over, I'm most likely going to be at 6x anyway!
Glass quality is impeccable of course.
I don't have much of a track-record on durability yet, as I just got it a short while ago. I will say though that durability was an initial concern of mine when shopping. It was one of the reasons I bought the Kahles. It is my understanding that Kahles concentrates more on the mil/LEO crowd, so durability is always a focus in their designs. I hope I'm not disappointed, but I don't expect to be.
Last but not last, the silky-smooth magnification ring and built-in cat-tail are very nice touches.
Now can you understand why I'm calling it the closest thing to optical perfection?
Buy the Kahles, and buy with confidence.