multiple alert as Google calendar does.
Even if I set a due date and its notification alarm, it never alerts me in advance and only give me an alert on the exact due date. When there are many tasks you can be forgetful or ignore the one time notification by just swiping it off. Then later you never get to know what's coming right until the due.
Of course you can set the alert for the time you want a notification but then you have to manually write down the actual due date and that's not pretty + inconvenient.