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It is true that if the adapter fails that you will be out of luck if you go with the ZE versions. As long as the adapter works, it would be just like shooting these on a Canon camera. You compose and focus at full aperture and the camera (and adapter) stop down to the aperture you have chosen automatically. I really like composing and focusing at full aperture, so I like that feature.
With the ZF/ZF2 you can still compose and/or focus at full aperture, but if you do you have to stop down manually using the aperture ring before shooting. Alternatively you can just compose and focus at the aperture at which you want to shoot. You can use full manual mode, but you can use aperture priority mode and let the camera set the shutter speed after setting ISO yourself. If you use auto ISO, I think you can also set aperture and shutter speed and the camera will set the ISO for proper exposure. So it isn't full manual. You can use aperture priority and you can use auto ISO. You just can't use shutter speed priority mode or presumably any fully automatic modes like P mode, etc where the camera needs to set the aperture.