Like Soulyss mentioned the P-39 we have seems almost without sin... It mushes through a turn like a P-38. Don't get me wrong it wallows badly but it doesn't want to depart as much as it should and it will just kind of hang there not getting anywhere fast but not falling out of the sky either.
The thing is Krusty, that when you tend to live on the limits of controlled flight, as some of us do too often, the P-39 can be diabolical. Perhaps worse than the P-40s, the P-39s have extremely abrupt departures. When down in the weeds, flaps out... Stability and predictability breeds confidence. It will take a fair amount of the P-39 flying to build confidence and develop the skill (really, more like "feel") needed to fly the edge without unwanted drama. Like the Ki-61 and P-40s, the use of flaps in a low speed scrum is probably not where you want to find yourself.
So, my advice to someone new to the P-39D is to fly it as previously described by others. Climb out to 10k or so, and fight down hill wherever feasible. Whenever possible fly as part of a pair or more of fighters. Why? Because, once you've burned through any altitude you had, you will be more defensive than offensive. You'll likely need someone to keep your six clear as you wobble off to regain some height.