Wow this thread has generated a lot of interesting debate.
First, just to clarify my own intentions: I'm not learning the Mustang simply to find a better aircraft; I'm learning it so that I can be competent in it whenever the situation calls upon it. I want to be able to fly the 'stang when it's listed in a pickup mission or in scenario or other special events. I also confess a curiosity about the bird because of its historical representation. As such, I am less interested in finding out whether it's a good or mediocre bird as much as I am in finding out how to fly it optimally. Were I to post about the 38 or the P40, my intention would be the same. I don't care if it's a good bird or not, I just want to be able to bring out the best in it when necessary.
That said, here are a few additional issues that I've discovered:
When buff killing or diving on an unsuspecting target, I am finding that it is harder for me to get a good guns solution. The Mustang has a different feel in a dive than my trusty FM2 or even the Dora, and as such, getting that quick kill is sometimes harder because I can't quite time the dive and/or get the deflection shot as well as I am used to. Again, this may be just a timing issue. I might need to change my angle of attack in order to compensate, but any advice would be helpful. My approach on low cons, or on buffs for that matter, is usually to dive from pretty much right on top of them. With the buffs I walk my bullets as I am diving, aiming for a wing root from a high angle and avoiding any dead six approaches. With low unsuspecting cons, I try to drop to a low six and come up just a bit to take the shot. In both cases I am either not getting enough hits for an instant kill, or I'm missing altogether.
What I have learned with the Mustang is to keep it fast, either above or at corner speed depending on whether I want to stay clear of the melee or engage more aggressively. I'm not going up and over as much as I am diving in, extending in a gradual climb to restore e and then coming back for another pass once I'm about 2.0 out from the target. As the con gets lower I start pressing the attack more closely, being careful to keep up my energy state as much as possible. I try to keep it at corner speed and wear the opponent down, and I'm finding that even slowed down a little, I have enough power to extend if I need to. It's when I'm below corner speed that things start to get hairy.
All in all, I'd say the Mustang can be very effective once you've learned its tricks. It's not necessarily my ride of choice, but it is no longer a bird I shun completely.
Addendum: I think with the buffs my problem is I can't make adjustments as easily as in the FM2. With the Wildcat, I usually have to adjust my angle upwards as I dive, i.e. as i come in I'm usually hitting the tail first, and I have to pull up a bit to bring the guns to bear on the wing root, unless of course I've lined it up perfecting on the first pass. With the Mustang, I can't adjust fast enough to get the bullets where I want them to go, and I don't quite have the timing to hit the wing root on the first pass.