I have read the drop rates are slightly better on Advanced Caster Training than Expert Training. Is this true? Seems odd for such a rare item that it drops better on the 30 ap than the 40 ap?
It's mostly due to AP efficiency, because both nodes already have such a low chance to drop it. The 30AP node roughly has 1.5% less chance of dropping hearts compared to the 40AP, but since it's not a large margin, you'll be able to spend AP and time better spamming it on the 30AP node instead.
Neither node is really worth farming in. Higher chance to get them during event runs where demon Lords are sure spawns. Can also appear in some strengthening quests. But in general event shops and event runs would be best (I need like 40 of them still to max ascend and skill up a few servants)
