I have just got the zoom a week ago and in the process shooting the first roll of film in landscape. It really impressed me a year ago when I tested drive it at the dealer. My mind had set for it ever since. (Not to mentioned this zoom has been named product of the year, or editor choice in numerous magazines).
First of all, I like the idea of having zoom for my medium format. As I have used zoom for decades and own all N zooms and pretty impressed with the Carl Zeiss zooms. I am planning to use it for landscape, street, people, studio, wedding, or even travel (if you believe it). I think I may be able to use it 80% of my time and not worry about carrying extra lenses. So, for the product point of view, it is a winner for me. Since I own the 35mm and 120mm lenese, this zoom is a good fit for my kit. I can keep my 80mm for my N1 as portrait lens. Also, I can share the 95mm filters with the 35mm and N17-35 lenses.
My first impression: I immediately start liking it as this morning I went up to Mt Diablo made a couple of shots before work. It made it so fast to take the shoots as I can utilize the zoom rather than moving in and out or changing lenses. I must tell you that I am not a fast shooter and like to take my time in general. Although the light was not very good but I still willing to try it. As if I shot 4x5, I would have just left because I didn't want to bother with the long set up time for the less perfect lighting.
For the TLA360 flash, I am sure it will cover it since 45mm is in equivalent to 28mm in 135 format. And the TLA360 can cover up to 24mm. I am going to mount the flash to the camera with this zoom to see how the TLA360 matches up the focal length automatically and run some test with the TTL flash. Judging from the setup, I don't thing the lens will block the flash.
I cannot answer if the lens is really superb yet. Something it can be subjective and depends on personal needs. I have mounted it on a tripod to play with it the first day in the studio, and I could see some vignetting at the corner from 45mm to 55mm. Stopping down didn't seem to correct the problem. It was just the observation from the viewfinder in a relative dark studio. The spec claims superb sharpness and brilliance, and I will run some test to keep you posted.
I think it probably not as good as the 45mm, 55mm and 80mm primes (at least on paper), even Carl Zeiss and some users claim it does. But I have learned to live with that for the trade off of the versatility of using zoom years ago.
In short, my first impression is very good. Well balance with the body, well built, distortion is very well controlled, and a very versatile lens.