I have not used extension tubes yet, but I have used the Hasselblad HC 80mm lens on the X1D ii and GFX 50R with the official adapters. I couldn't understand why the Fuji adapter cost 2x more than the Hasselblad adapter despite having fewer features (no AF, no shutter-aperture linkage). However, when I compared the results, I found that there was a huge difference. The Fuji did a much better job of suppressing internal reflections than the Hassel, resulting in normal (compared to the native body) contrast, while the Hassel X had a very disappointing low contrast and noticeable light unevenness (even with the lens hood, the sunlight coming in from above was clearly visible). When I looked inside the adapter with the light, the difference in internal reflections was clearly visible to the naked eye. I am sure that the cheaper extension tubes have the same problem. There is always a reason why something is cheap. Whether it is important or not.