Do not use summoning scroll AT ALL until you have collected all purple and blue ones.
Because if you get one in a scroll, you can't farm the node, whereas if you farm the node, you can get both the summon AND some other random drops. Furthermore, if you get the summon in the scroll after that, you get summon point out of the dupe.
Farming node is free, takes awhile but free. So farm them all THEN use summon scroll (maybe wait for a summon rebate event at that)