Miscorrection for the blue scribe there some spells from the BRB they can not use at all and there for get to re-roll i will tell you what ones they can use and cant (Note that the Blue Scribes are not psykers for the purposes of any special rules that target Psykers)

Biomancy
Can use 2 3 6
Cant use 1 4(to half the effect) 5

Divination
Can use 2 3
Cant use 1 4 5 6

Pyromancy
Can use 2 3 4 5 6
Cant use 1

Telekinesis
Can use 1 3 4 5 6
Cant use 2

Telepathy
Can use 1 2 3 4 5 6

See how less random Divination is compared to the others and how most of the character spell casters have Divination as there secondary abiltys both are great no matter what one you get Re-roll Failed to hit or force your enamy to Re-roll saving throws + warpflame toughness tests feel the burn :P