Mustangs are excellent planes, but they are way over-hyped.
It's a generally very bad plane to fight in when you don't have either numbers or alt advantage, and the only truly amazing capability that ensures its survival is the dive-and-run factor. Doesn't climb too good, doesn't accelerate too good(however, a slight dive gives out very good acceleration), doesn't turn well. In a 1v1 situation I'd guess the Bf109G-10 would dominate the fight most of the times unless the Mustang had something like a 5000 feet altitude advantage.. and even then, one good lure&bait and the Bf109G-10 can turn the tables quickly.
However, when they are working in groups at high altitudes over 15k, retain alt advantage and keep their speed up high, they are very versatile.
Capable plane, but over-hyped.