I am sure flying on one engine is fine.
However, it would be interesting to have a video of cockpit during these operations.
I remember reading years ago about these ETOPS and they mentioned a case when a twin had control problems on one engine(poss bleed valves stuck open) and only about 50% power avail on that engine, this was OK.
But other engine had oil leak and crew noticed oil reducing, they diverted very quick and all was OK.
Think after crew noticed leak, engine had about 75mins left till out of oil.
Lucky they were not on the 207 time zone when this occured.
Think it was a PAN AM A310 in the early 1990's, does anybody have the details.