I really like the extended rectangle of 6x9, and have not only optional 6x9 roll film backs for my 4x5 cameras, but also GW690ii and GW690iii cameras. If I want a 6X7-ish image instead, I just crop. I do have a Pentax 6x7 kit too, which is especially nice for telephoto work, along with full 4x5 and 8x10 sheet film systems. I would have gravitated to 5x7 sheet film if it had been more commonly available in color. But I can always crop 8x10 images narrower too if necessary. It's all good. What I particularly like about the Fuji RF's is that I can shoot them either on tripod or handheld, which is really nice if the wind is howling, or in a blizzard, or if I just need to work really fast and spontaneous. And so far, they've held up well in really bad mountain weather. These Fuji RF cameras also have superb lenses.
But squarish Hassies etc deliver just too small an image area for my own enlargement needs. 6X9 has twice the area as a 6x6 equipped with a typical 645 rectangle back. Not, not as nice as enlarging from full 4x5, but a reasonable convenience or compromise format. Roll film is a lot cheaper to shoot too.
Big? That's all relative. A Fuji 6x9 RF is the smallest camera I ordinarily work with. It's no heavier than many 35mm SLR's; lighter than some. Fits in a reasonably small shoulder bag. Handholds better than my NIkon, and I have unusually small hands!