Tamron 18-400

What do you think about this lens?!

Any reviews?!

HAND.

Mike Jackson (Best of the Tetons) used this lens on his D500 several years ago, with excellent results.

I used to have one for Canon and used it on the M6 as main travel lens.
It did not balance nice with the small body and, I had to use additional EF to EF-M mount adapter in order to use it.
At the beginning, I had a lot of fun going so quickly through the vast focal range, and the option of creating nice detail shots/closeups of plants and flowers. I loved its convenience so much!
However, after editing the first serious travel picks, I noticed that at the wide setting the corners were unacceptably soft for architechture subjects.
IQ for nearby subjects was good to very good, but no so good for subjects at larger distances, e.g. a building from some distance.
The center of the lens is decently sharp at all but at 400mm focal length. AF was slightly slower than native zooms and not as reliable on some occasions, especially at tele end.
I didn't detect that during my test drives which were mostely nature and park related.

Durig the pandemic, I bench marked all my lenses vs. Sony RX 10 IV. The Tamron 18-400mm lost on all accounts and had to leave my camera bag again.

I do not have a review on hand, but I have this lens and have used it quite a bit on a D7500.
It is decently sharp (especially for the zoom ratio) on the tele end, while the wide angle leaves much to be desired, though of course it improves when stopping down.
If you need the longer zoom, make sure to have a lot of light or boost your ISOs, otherwise the image will be poor. A lot of sunlight, high shutter speed and f/10 gives great pictures!

In my opinion it is very convenient for e.g. hikes when you do not want to be changing lenses often. I have used it under pouring rain and snow (with a defective raincover to protect it, though) and it is still in great shape, which means it is very good as a do-all lens.
The VC (VR) is not very good, iirc it is rated for 2.5 stops or something; it slightly increases the rate of keepers but I would not want to change the auto iso speed based on it.
The focusing ring that moves when autofocusing is quite an annoyance (since it is often where my hand is).
I am sure some people only have that lens on their camera, but to me it is a compromise, and I need a few other lenses for situations where I want better IQ/light/etc. 18 on the wide end is also a bit narrow sometimes.

And you need to be shooting RAW and correct distortion with darktable or another tool for proper picture display.

My advice would be to try it if possible (the downsides are quite easy to pick up) and see if the compromises are worth it for you.