score:8
Local resident here.
As some commenters pointed out, this is a bus run operated by a private company on behalf of Trentino Trasporti. Apart of the livery of the car, there is basically no difference. You can use the same tickets.
I don't know why they put this note on the timetable, probably to warn tourists that they have to expect a bus with a private company logo instead of the "Trentino Transporti" one. There will be a paper sign on the windscreen with the logo of "Trentino Trasporti" and the destination. Usually it is quite noticeable, so it's difficult to make mistakes.
Reservation is not possible for individuals; for large groups the best thing would be to call directly Trentino Trasporti for it might be not possible for all routes and hours.