I have just begun to use it, and I still have a lot to learn. These are my first impressions.
There is a lot of conflicting and misleading information about this camera on the internet. Mine is updated to Firmware 1.50, and with that update, the camera gains a fully electronic shutter, but with one peculiar behavior. In Live View, on a fully open lens, the exposure is taken without any sound or vibration. The mirror stays up all the time. Great! But as the camera begins to write the file to the card, the mechanical shutter does close, and it opens again after a short delay. It is an insane behavior. The same happens in pixel-shifting mode: the camera silently takes four pictures, and then the mechanical shutter closes and opens. For most macro work, this does provide the vibration-free photography we hope for. However, the extra vibration after the exposure can cause a subject in liquid to move slightly between frames of a stack. If I had known of this behavior, I may not have bought the camera.
There is also no information on the internet about how long it takes to capture a pixel-shifted image. I found that it takes about 14 seconds, exclusive of [shutter speed x 4], to capture and write the image onto a fast SD card. That's a long time if a big stack is being shot. A 200-image stack (typical for me) would take almost an hour to shoot, which is quite long, especially if the subject is alive like a plant. So the pixel shifting has some major practical limitations. The capture time can be reduced to 8s per shot if only a jpg is being saved to the card.
I want to use microphotolithography lenses and monochromatic light, and a pixel-shifting camera should have vastly more resolution than an ordinary camera in that case, so I would probably still have bought this even if I had known how long the pixel shift capture takes. But for most stackers, I think such a slow pixel-shift capture would rarely be worth the trouble.
I have lots of Nikon lenses and no Pentax K mount lenses. No direct Nikon to K mount adapter is possible, because the flange-to-sensor distances of the two mounts differ by only a millimeter. There are adapters that add an extension and incorporate a lens to get infinity focus, but these are optical garbage. I stripped out the insides of one of these, to give me an adapter that lets me use Nikon-mount lenses that focus by pure extension. But my plan is to replace the Pentax mount with a Nikon mount, probably using parts from the Novoflex Nikon-to-Canon mount that I have. Then the camera will be much more useful. But a Sony A7Rii would have had no conversion problems of any kind. So again, unless someone really wanted pixel-shifting badly, the A7Rii would be a better choice.
There were some complaints on the internet about the difficulty of using Live View and getting good metering data with non-native lenses. I have not found that to be any problem at all. There's a green button that sets the exposure so that it looks just like the Live View image, and at least with the subjects I've tried, it works perfectly.
Here are my first stacks of jpgs, using the default settings of the camera, which make for rather flat images. The default settings can be finely adjusted, except for the most important one, the degree of compression. I made normal and pixel-shift stacks. At this magnification, the normal and pixel-shifted images look the same.
Below are 200% enlargements of the yellow-outlined portion of the image above: on the left is an enlargement from the stack of normal images, and on the right is an enlargement from the stack of pixel-shifted images. (These were made from 100% crops which were then enlarged 200% using "nearest-neighbor" extrapolation.)
Here is the same at 400% enlargement:
The virtually identical current price tag makes decision even harder...