What are the experiences with refunding ongoing DONEx ticket? Can they (e.g. QF) calculate the remaining amount easily, and are there any pitfalls apart from the 5% fee? I'd like to ask how they calculate it in the first place but :-)

We have done EUR-APAC-ASIA legs with ASIA-to-NA, local NA, and back to EU flights remaining and for our travel needs, cancelling the ticket is a viable option.