for some reason i think that the orb would be better for a lower level because just having a bunch of focus wouldnt be good
you would have to be able to also REGEN that focus too
otherwise it would be a little boring going on a killing spree for a bit until all your energy is used
then waiting a super long time for all that energy to be filled up again
for the higher levels though i think a grimoire would be better
just my opinion though

Well I was thinking exactly the opposite lol.
If you have the cash, I would.
Use grimmore in early lvls bc we don't hav much stat points at that time, low foc= significant increase in spell dmg with grimmore. 15 tick is enough for low lvls b/c energy consumptions are relatively low.
Use orb in late lvls bc we should by then have plenty of foc, so much foc that adding more wouldn't make a lot of difference to our spell dmg, to compensate for the waste of extra foc from grim, change it to orb, gives 25 tick which you would need as energy consumptions in later lvls are really high, and skill evasion bonus would be more useful as mobs would generally use skills (duh) at later lvls.