Folks need to look beyond a few minor issues in post processing, please...
The Dual Exposure feature in the IQ4150 is impressive, to say the least. I have never found any exposure tool that allows the ease at which you can now work a single file. Where as before you needed to combine multiple exposures in post with different types of software to get somewhat the same level of response.
Sure this file has some processing issues to many folks, to the poster maybe not.
C1 has a basic tendency to create a highlight halo effect on sky silhouetted subject matter, it's something that I have pointed out to C1 developers and my dealers for years. As pointed out the trees show it quite a bit and that is very easy to control in C1 once it's noticed. I personally don't find the issue of the horizon line that big a deal, don't even notice it for the entire horizon. Again something that can be easily fixed. The Dual Exposure raw, doesn't look like this, and doesn't create these highlight over processed issues, these were created in post.
Neither of these issue take away from the fact that you now can expose for a sunset by checking exposure on the sun and then shooting the image, never working about a bracketing sequence, and vastly removing the issue of movement artifacts. You still can see some of them in this image on the right side, but with any exposure at a certain speed movement is just going to happen.
The fact that you have over a 3 stop push in the foreground is what impresses me, and that this same 3 stop push works at base ISO or ISO 400, extremely clean details that would have other wise been effected by noise. The only real issue I see that was created by the dual exposure was the areas in the sky mainly on the right side where the tool did not get a clean blend. I have seen this with my images, more so where you are really pushing the tool, but they are easy enough to correct in CC with content aware and only seems to show up in the sky or other solid areas.
Phase One again, missed an opportunity to showcase this feature as it was again left up to local dealers to take images and then show them to the public. But after using this feature now, I can strongly state that it's a major advantage to standard bracketing, much less work, and for my style of work addressed what frame averaging missed, (motion issues creating artifacts), not to be confused with normal motion blur.
Take it for what you wish, but the feature offers some major positive advantages, especially for a landscape photographer.
Hopefully other companies with BSI chips/Sony et all can add a similar feature to their cameras.
Paul C