Metal gears are nice --
However -If you never slap the ground hard - plastic gears are better - tighter- longer .
If you run long servo arms and smack down the landings -you should use metal gears.
We run plastic gears on lots of 33% aerobatic stuf but the thumps are what get em - I accidently kicked a rudder -with the radio on and -there went both sets of gears on 8411SA -So I swapped to 8411 gears