There's really little functional difference between them. The use of the progressive tense always implies some kind of temporal relationship, but (I think) with instantaneous events it's a "difference that makes no difference".
"Finished" or "completed" can be similar:
I'll clean my room once I've finished breakfast.
I'll clean my room once I finish breakfast.
Only once Luke has completed his training, will he be ready to face the Emperor.
Only once Luke completes his training, will he be ready to face the Emperor.
As well as other "instantaneous" verbs like "pass/fail".
Once you've passed History, we can talk about summer camp
One you pass History, we can talk about summer camp.
I'm sure you can think of others.