I didn't see any tenebrium 2 weapons until around level 16-17 or around the hunter edge time of the game. It was a bow that would have been somewhat better. 200 phys, 40 elemental, 40 tenebrium. Higher than my crafted bow of 220 physical.
For what it's worth, my ranger is at level 16 and I've just crafted a bow for him with a maximum of 234 physical damage and an addition 70 tenebrium damage (along with a +2 speed gain). I haven't yet come across a bow that does more, so I'm still assuming that crafting is generally your best option, damage-wise.
To use it, a single point in tenebrium is sufficient. However, as Stabbey said, you do need 3 points tenebrium to craft it.
