I just decided that I'd rather spend £400 on a bike box which might get battered but which would last at least (say) 10 holidays, and be fairly certain that my my £2,000 bike and £1,000 holidays weren't going to be ruined, than save the money on the box and risk a cardboard box/bike bag again.
I think I've had about 7 holidays using the SciCon box now. Each holiday that goes by reduces the effective cost of the box per trip. It would be very easy for £400 worth of damage to be done to a bike on a single flight.
I can't remember where I saw it recently, it could have been on CycleChat or elsewhere, but I saw a picture of someone's bike after he picked it up at the airport and it was really mangled. The drops were bent round so far, it looked as though a fork-lift truck must have driven over the bike!