I turn way better with manual trim when I set it to max nose up, and same tweak saved me from many compressions in 109 and La's.
Also when you compress and still want to try a cherry picking, nothing is better that manual trim to counter the nose up tendency, and still have a precise shot at high speed.
Another thing I saw with combat trim is that it plays with your roll rate (ailerons) and before I used manual I never noticed that some planes roll better in a way that the other....and yes another thing, combat trim plays with rudder also, resulting of rudder changes while diving on ground target, wich gives a weird feeling especially in F4U in wich I suspect the rudder to compensate for torque on low speed climbing.
And you said it for E managment manual trim saves some E, and you feel better your plane, example you can feel when the spit "climbs like a wing" at low speed, giving better chances for rope etc....
On the take off landing part I never had trouble, and it can be nice to use manual to keep F4U nose up while landing etc.
About the stability I've had some problem but figured I was tryin to shoot while being to slow, focused on my zoom. Maybe combat trim can help in this....
One con is when when you calbrate your trim for the diving speed and have to pull stick like mad to climb when slower....its a reflex to have and personnally I changed all trim controls to be close to view/flaps controls.
On another subject I think default controls aren't optimized at all and advanced players should think about a remap, I've done it and not to have to move the left hand allover the keyb in dogfight is a great time and life saver.
I hope my text is nearly understandable and will help you