I finally had the chance to use the first stabilized 24-70/2,8 in the history of mankind.
Unfortunately, being the focus ring at the bottom of the lens, using it on a rig with a follow focus, as I suspected, is not comfortable at all and that's already a "no go", for me. Anyway, I considered to keep the lens anyway, even if it could not replace the Canon 24-70/2.8, for times when I have to act fast and use the camera on a monopod or even handheld. But... VC doesn't work, at least on my sample, as well as it should.
I noticed it shooting stills, but this makes me suspicious about its video skills too.
What I noticed is that it takes a while for the VC to start working after you half press the shutter button, so it is not very helpful if you have to to take a picture "on the fly", like during an event.
What's more, with faster shutter speeds (let's say over 1/60) if I leave the VC enabled I get less sharp images than if I keep it disabled, so I always have to check the shutter speed I'm using to decide whether to live the VC enabled or not. Way too annoying.
After a couple of days of testing, I brought the lens back to the shop. They told me than in a week they'll give me another copy to verify if this issues are to be considered "normal", but I think I already made up my mind.
As far as the optics is concerned, that's definitely a very good lens, considering its price, but the mechanical side leaves a lot to be desired, as often happens with third-party lenses. And I'm also afraid, from what I read in many posts, that QC is quite an issue at Tamron's. I don't wanna have to test 3-4 lenses before getting a decent one and keep worrying that it could suddenly stop working properly...
Anyway, I will check this second sample before deciding.