Looks like
it landed an hour or so ago.
It on par in terms of atmosphere (cabin pressure, humidity, etc), quieter and roomier, particularly in economy. Dreamliner is awfully tight in economy, unless you're flying JAL - only airline with 8-abreast seating.
They can. The aircraft are leased, as are the A340s they replace. The A340s are great aircraft and vastly cheaper to operate than the 747s before them. But they can't compete with modern 2-engine wide-bodies. The A350s will save SAA a lot of money.
Flying isn't exactly gambling though. Despite what you might think of their management and profitability, SAA has very good and well earned safety record, and operate a long haul fleet with a perfect safety record.