Thanks. I do want to use the voucher on both legs so bookings would need to be joined but I’ve also had the experience of not being able to get an agent on the phone at 0100 so am considering pros and cons.

Good point about cancellation/change fees. That could become a bit punitive.

I had read on this forum (earlier in this thread I think) that in some cases (USA, I believe) the taxes worked out more expensive to have two one-way booking. Was just trying to work out if that might be the case for Tokyo booking, currently RFS in J. Aiming to snap F seats if ever they were to be released. Unlikely!