In my experience Z10 is not that shiny at all. Some actually add some Z-16 (10-20%) to get more gloss. That is what I tried when I detailed this Lexus IS350 w/ cashmere interior. As you can see the seats do not look shiny at all.
No it is not shiny. That's why I use it. Leather feels great after Z9 followed with Z10 leaving a great naturally smelling leather. The Z10 is liquid and water based conditioner.
I doubt if your new leather needs any cleaning, if it does in spots use Z9. IMO I think you will be fine using Z10 on new leather. Its not going to hurt anything....