I've little doubt that they perform admirably for the airline and return a pleasing passenger experience. But as a Contoller I bl@@dy hate them! The -300's are undoubtedly worse than the -600's but the rates of climb are a joke.
A few weeks ago the South Africa bound Heathrow flight reached the dizzy heights of FL280 as it passed Paris. With continuous climb and a little creative vectoring by my good self to avoid a high sided goods vehicle on the Brighton ring road.....