Byrna
point being, a faster aircraft with less range would have to stop, while the slower but longer legged 340 cruises on overhead while the other plane is being refuelled. Introducing a 343 onto YVR-SYD has saved Air Canada a fuel stop southbound and this route is enjoying very healthy business.
As to disadvantage - most complaints about 340s seem to be about climb performance from ATC - a China Airlines 340 took off from an ANC taxiway so takeoff performance isn't so much of an issue
With the 340 as with all 4 engined aircraft, you lose one engine means only 25% power down which is, in theory, safer than 3 or 2 engine equivalents, but no more so than 744. Safety-wise I don't recall any fatal incidents involving a 340 in 14 years revenue service, but I am open to correction.