There is a whole world of UV ink adhesion the machine manufacturers will not tell you. There is a reason that Sericol has a whole line of adhesion promotors for UV inks for different materials. It will print on anything but it will not stick to anything. We've done thousands of materials, and some coro will come off easily, glass is a no-no unless you get a specific type of glass, aluminum can come off easily if not prepped, etc, etc.
The other option is profiles, if you want better color, you put down more ink...but with UV, it will lie to you and it will look cured but really it's just the top layer curing and not all the way through, so you want get good adhesion to the substrate. You have to find the fine line between good color and good adhesion, it's a give and take.
I would go with the Durst, one of the best machines out there hands down...I know huge companies that would scrap their 4 Vutek's UV in 2 secs before they ever had to scrap their one Durst.