Thanks for the helpful replies so far! Definitely happy with the price I'd be paying at the moment so might go ahead and get them. Good 40% cheaper than my return to Australia last summer, so can't complain.

Only remaining issue is that the Economy Saver doesn't let you pick your seats until online check-in opens. My better half is booking a different set of flights with the aim of returning on the same flight from Bali as myself. How (un)likely is it that we'd be able to get seats next to each other if we booked separately? I'm reluctant to pay for Economy Flex as it's a good £300 more expensive than Saver is, plus I tend to sleep all the time on flights anyway...