"I would guess there is a slight fuel saving per approach"
I seriously doubt that.
"There is no suggestion that 3.2° RNAV approaches will be mandatory for any arriving flights. The conventional ILS, MLS and 3° PAPIS will continue to be available.
Pilots will, as usual, request their desired type of approach (ILS, Microwave or the trial 3.2° "RNAV Yankee") on first contact with Heathrow Director."
It's a trial. How could you do a trial if you have no data to compare with. I have some faith airport bureaucrats can actually measure noise, and publish the data. Yes, people who buy a cheap property but don't like aircraft noise can seem a bit annoying, but if a 3.2 approach would help, why not give it a try.