Just tried it on a complex model I did last year with 3ds Max. Many curved shapes, many tiny islands. Back then UV packing was done with PolyUnwrap and lots of manual improvements. I don’t know any more how much time I spent on it but it must have been one or two hours at least.
According to UVPackmaster I achieved 65% coverage. 2 minutes of recalculation later: 73%. This is awesome.