Basically..
Apprentices' benefit: receives prizes every 10 levels up to level 40 (10, 20, 30, 40). Prizes are usually just a pet, a weapon and the like though (nothing too 1337). After 40, apprentices don't get anything from it.
Master's benefit: receives 10% of what apprentice spends on NPC. This usually doesn't count for much at low levels though. I think it pays off more when your apprentice is like, level 50-60+ LOL.
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